The latest explosive Epstein revelations first forced him to resign from his beloved Labour Party, he said, to save the party from "further embarrassment".
But then the furore over the disclosure that he leaked highly confidential and market sensitive information to Jeffrey Epstein while he was business secretary under Gordon Brown was worse than embarrassing.
It led to calls for a police investigation over allegations of misconduct in a public office, which the Metropolitan Police is currently reviewing. Brown's allies called it a "betrayal of trust" and some MPs accused Mandelson of treachery.
Then, after the prime minister told the cabinet Mandelson had "let the country down" and should no longer be a member of the House of Lords or use his title, the disgraced now former peer threw in the towel and told new Lord Speaker, Lord Michael Forsyth, of his "intention to retire" from the Lords.
There's no way back now. He's finished. And he could yet face prosecution and - potentially - jail, if convicted.
It’s difficult to imagine what could be more embarrassing than this weekend’s disclosure of payments by Jeffrey Epstein to his then partner, lobbying a Labour chancellor on tax policy and being photographed wearing nothing more than a T-shirt and a pair of underpants.
And the resignations must have been a horrible wrench as well as a humiliation for Lord Mandelson, who had - as he lamented - dedicated his life to the Labour Party.
A scandal-tainted career
Indeed, he was born into the Labour Party. His grandfather was Herbert Morrison, one of the giants of Clement Attlee's post-war government.
But it was his attraction to the rich and famous and his fondness for the trappings of wealth that brought about what will be the final downfall of his scandal-tainted career.
He famously told tech executives when he was Sir Tony Blair's trade and industry secretary in 1998: "We are intensely relaxed about people getting filthy rich."
Then, acutely aware of the risk of damaging headlines, the former spin doctor known as the "Prince of Darkness", added hurriedly: "As long as they pay their taxes."
His final demise comes just months after Sir Keir was forced to sack him from the top diplomatic post of UK ambassador to the US over his association with the convicted sex offender Epstein.
But Epstein was by no means the first Mandelson scandal. He had to resign from Sir Tony's cabinet twice, first over an undeclared bank loan and then over intervening in a passport application by a top Indian businessman.
A controversial and divisive figure
Over four decades, nearly all on the frontline of British politics, he was a consummate political networker, but also one of the most divisive figures in public life and his appointment as ambassador was seen by critics as an act of cronyism by Sir Keir.
Acknowledging that Lord Mandelson - awarded a peerage in 2008 by Gordon Brown - was a controversial and divisive figure, Sir Tony declared in 1996: "My project will be complete when the Labour Party learns to love Peter Mandelson."
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The Washington role is seen as the most glittering and important diplomatic post in the UK government. The perks of the job include the luxurious ambassador's residence in Massachusetts Avenue, a magnificent Queen Anne mansion designed by top architect Sir Edwin Lutyens.
When he appointed him as ambassador, Sir Keir saw Lord Mandelson as a skilful and persuasive link to the president, with his trade experience from his time as a cabinet minister and Brussels commissioner a vital qualification for the job.
Never one for false modesty, Lord Mandelson claimed that when he first walked into the Oval Office the president said to him: "God, you're a good-looking fellow, aren't you?"
Diplomatic triumphs
Lord Mandelson was credited with several diplomatic triumphs in Washington. He played a vital role in ensuring the UK escaped the worst of Trump's tariffs and he was instrumental in securing a much sought-after trade deal between the UK and the US.
And his silky PR skills were displayed when during Sir Keir's first visit to the White House in February, the PM theatrically pulled out of his inside pocket a letter from King Charles inviting the US president to visit the UK.
It was a classic Lord Mandelson stunt and confirmed he'd lost none of the flair for presentation he'd first deployed when he was Labour leader Neil Kinnock's spin doctor in the 1980s.
Lord Mandelson's high-profile political career began as a TV producer until his appointment as Labour's director of communications under Kinnock in 1985.
He was seen as a brilliant if ruthless spin doctor, who masterminded the birth of New Labour but would berate newspaper editors when unfavourable stories were written by their political journalists.
Another classic Lord Mandelson attempt to kill an embarrassing story was to tell the journalist who wrote or broadcast it in a sneering voice: "That is a story that I believe will remain an exclusive."
He became MP for Hartlepool in 1992 and helped propel Sir Tony to the leadership of the party after John Smith's death in 1994, a move that led to a bitter feud with Mr Brown.
There's an amusing story about Mandelson in Hartlepool, which he claimed is a myth and blames Kinnock for. It's claimed he ordered "some of that delicious guacamole" in a fish and chip shop, mistaking mushy peas for avocado dip.
It was a perfect Mandelson story, ridiculing his metropolitan tastes and ignorance of working-class life. But he claims the mistake was made by a young American woman student who was helping Labour's campaign.
'I'm a fighter, not a quitter'
His first cabinet job, trade and industry secretary in 1998, lasted only five months after he was forced to quit after failing to declare a home loan from Labour millionaire Geoffrey Robinson to his building society.
His resignation was similar in one respect to the demise of former deputy prime minister Angela Rayner last year, in that it was over irregularities in buying a property: in Hove in her case, in fashionable Notting Hill in his.
He bounced back as Northern Ireland secretary in 1999 and was said to enjoy the luxury of Hillsborough Castle, which went with the job. But he was forced to resign a second time over claims he helped businessman Srichand Hinduja with an application for UK citizenship.
When he held his seat in Hartlepool in the 2001 general election, Mandelson made a passionate and defiant victory speech at his count in which he declared: "I'm a fighter, not a quitter."
Yet three years later he did quit as an MP, when he became a trade commissioner in Brussels, serving a four-year term during which he had a spectacular row with French president Nicolas Sarkozy, who accused him of selling out French farmers in trade talks.
There were more controversies arising from his time in Brussels. In 2006, it was reported that he received a free cruise on a yacht from an Italian mogul who was said to have benefited from tariffs on Chinese shoes when Mandelson was EU trade commissioner.
Reports also claimed he had been lent a private jet by banking and business tycoon Nat Rothschild. And it was later reported that he had a holiday in August 2008 on the yacht of Russian oligarch Oleg Deripaska off the Greek island of Corfu.
Mr Deripaska was said to have benefited from a cut in EU aluminium tariffs introduced by Mandelson. But prime minister Brown said Mandelson's dealings with Mr Deripaska had been "found to be above board".
His political comeback
After Brussels came perhaps his most spectacular and unexpected political comeback, when in 2008 his old foe Brown, by now prime minister but facing challenges to his leadership, brought him back as business secretary with a peerage.
A year later, Brown awarded him the grand title, previously held by Michael Heseltine under John Major, of first secretary of state, a position he held until Labour's election defeat in 2010.
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To the end, Lord Mandelson remained a devoted Blairite rather than a soulmate of Mr Brown. And in the run-up to Sir Keir's 2024 general election victory last year, he was back in the fold, offering advice on campaigning and policy.
He got his reward with the plum job of ambassador in Washington. But his links to a very American scandal, involving the disgraced financier and sex offender Epstein, pushed him out of political life.
He may have hoped for yet another comeback, but that won't happen now. There are calls from opposition MPs for him to be stripped of his peerage. Currently on leave of absence from the Lords, he says he doesn't plan to return.
But what will hurt him most will be being forced to sever his link with the Labour Party that he was born into and which he served all his life. Until now. It's over.
Two people are believed to have been on board the plane.
The crash happened in the Littleborough area, and emergency services are at the scene.
A statement from Greater Manchester Police said: "Emergency services are responding to reports of a light aircraft crash in the Littleborough area.
"We are currently in attendance to establish the full circumstances and assess any casualties.
"A scene is in place whilst emergency service workers conduct their enquiries and people are asked to avoid the area as this work is carried out."
Photos shared on social media appear to show a yellow parachute partly wrapped around the base of an electricity pylon.
There are reports that the aircraft which crashed is a Cirrus SR20, a plane which is fitted with a parachute system designed to deploy in an emergency.
The flight tracking website, flightradar24, posted a message on X showing an image of a Cirrus aircraft, believed to be involved in the accident.
It said a plane departed Birmingham Airport at 9.59am and the last signal was received at around 10.39am "south of the M62 motorway near Marsden". It has not officially been confirmed whether this is the aircraft which crashed.
A Birmingham Airport spokesman confirmed a private light aircraft left its XLR Executive Jet Centre at around 10am on Tuesday.
Other images from the scene show a large response from the emergency services, with several fire engines, police and ambulance vehicles.
The Air Accidents Investigation Branch (AAIB) has issued a statement related to the crash.
"An accident involving a light aircraft which occurred today (3 February) near Rochdale, Greater Manchester has been notified to the AAIB.
"An investigation has been launched and a multidisciplinary team of inspectors are on their way to the accident site."
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Part of the A379 in Devon, connecting the villages of Torcross and Slapton, near Dartmouth, broke apart overnight, with its sea defences destroyed in January's three named storms - Goretti, Ingrid and Chandra.
The storms all brought heavy rain to many areas of the UK, particularly the South West, leading to flooding and widespread travel disruption.
Read more: Rain alerts for southwest in already flood-hit areas
Images from the scene show that sections of the road, and a public car park, have disappeared into the sea.
Devon County Council has warned that the damage to the A379 could cost "tens of millions of pounds" to repair, while Liberal Democrat MP Caroline Voaden said: "This is the news we've all been dreading."
Ms Voaden, the MP for South Devon, who was at Westminster to urge the government to provide more funding for roads on Tuesday, said earlier: "One of my team is on the ground now, and said the force of the waves is shaking the road. It's terrifying."
She also said: "Protection measures are needed, but government support is simply not there.
"Billions have been dedicated to Northern Powerhouse Rail, while our coastal communities are left defenceless to our changing climate."
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Devon County Council leader Julian Brazil, also at Westminster, said in a statement: "It's devastating for the local community, and our priority is the families whose lives and livelihoods are directly affected by this.
"The route is not looking good, and we're likely to be looking at tens of millions of pounds to repair it. The county can't afford to rebuild the road, and we're desperately looking for help from government."
The road was previously washed away during Storm Emma in March 2018 - also called the Beast from the East - and reopened later that year after extensive repairs.
Ross Brogan, 31, bombarded four teenagers with indecent communications and obscene videos, then offered payment to reciprocate.
The Crown Office and Procurator Fiscal Service (COPFS) said the software engineer, from Glasgow, befriended the boys via Snapchat and quickly tried to exploit their friendships for his own gratification.
Prosecutors told the city's high court how he demanded intimate images and videos of the youngsters - all aged under 16 - in return for Xbox or PlayStation codes which would allow them to make purchases via their games consoles.
In his sentencing statement, Judge Bruce Erroch KC said Brogan adopted an assumed identity on social media and contacted a boy he personally knew.
The judge stated that the worried victim confided in Brogan, unaware he was behind the sexually explicit requests.
Judge Erroch said it culminated in Brogan committing oral rape on the boy.
The judge stated: "It is difficult to conceive of a more calculated course of deceit and manipulation."
COPFS said Brogan also left sex toys at a pre-arranged drop-off point, instructing that they be used in indecent photos and footage which should be sent to him.
Judge Erroch noted how he also threatened to hurt one of the boys and his family if he refused to obey his twisted demands.
Brogan pleaded guilty to six sexual offence charges at the High Court in Glasgow last month.
He was handed an extended sentence at the same court on Tuesday, with 10-and-a-half years in jail and an additional three years on licence once released back into the community.
The judge acknowledged his lack of a criminal record and apology, but said the harm caused to the boys was "significant".
He told Brogan: "You are a mature man who chose to act as you did.
"Your actions were clearly planned, were calculated and were the opposite of spontaneous."
Brogan was also banned from contacting his victims and had his name added to the sex offenders' register indefinitely.
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Procurator Fiscal Faye Cook branded Brogan's behaviour "predatory and despicable".
She added: "He targeted young boys and exploited them for his own depraved ends."
Detective Inspector Stephen Palmer said: "Brogan is a depraved sexual offender who gave no thought to his victims, just using them for his sexual gratification.
"These boys have been deeply impacted by his actions and I hope this sentence brings them some comfort.
"I want to acknowledge the strength of all who provided information to police in this case. Brogan's conviction is down to them."
Austin Appelbee was with his mother, brother and sister on an inflatable kayak and paddleboards when they got into difficulties on Friday as strong winds picked up off the coast of Western Australia.
Desperate to get help, Joanne Appelbee, 47, asked her son to swim around 4km (2.5 miles) to shore.
Austin told local broadcaster ABC: "I was very puffed out but I couldn't feel how tired I was. I don't know, I was more thinking of a lot of things that, you know, was happening in my life.
"I think at one point I was thinking of Thomas the Tank Engine, trying to get the happiest things in my head... not the bad things that'll distract me... at this time the waves are massive and I have no life jacket on. Anyway, I just keep swimming."
Austin said he initially set off for help on an inflatable kayak that was taking on water. He abandoned the kayak and then took off his life jacket because it impeded his swimming.
The family, from the state capital, Perth, found themselves stranded with only lifejackets and no means of communication.
They had to wait 10 hours before rescuers reached the group, which included Austin's brother, Beau, 12, and his eight-year-old sister, Grace.
"We kept positive, we were singing and we were joking and... we were treating it as a bit of a game until the sun started to go down and that's when it was getting very choppy. Very big waves," Joanne said.
Scariest moment ever
"Ten hours we were out there, and I think definitely eight and half of them were the most scariest we've ever been through ever," she added.
Austin also said his ordeal was not over when he finished his swim.
"I just keep swimming... and then finally I just made it to shore and I hit the bottom of the beach and I just collapsed and then after that I had to sprint two kilometres to go get to the phone."
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Mum: 'Super proud'
Mum Joanne said she was "super proud" of her son and was just grateful the family survived being stuck so far out to sea.
"To keep going for so long... he's absolutely amazing. Me and his dad are super proud.
She said: "One of the hardest decisions I ever had to make was to say to Austin, 'try and get to shore and get some help. This could get really serious really quickly'.
"We made it, we're alive and that's the most important thing, and I have all three babies. All three of them made it. That was all that mattered. It was good."
A search helicopter found Joanne and her two children wearing life jackets and clinging to a paddleboard at 8.30pm (12.30pm UK time), police said. They had drifted 14km (9 miles) from Quindalup, where they had originally entered the water.
"The actions of the 13-year-old boy cannot be praised highly enough - his determination and courage ultimately saved the lives of his mother and siblings," Police Inspector James Bradley said.
The teenager survived his ordeal relatively unscathed, needing only a crutch to help his sore legs bear his weight.