The BBC gave few details about his sacking on Monday, only that Mills had been dismissed due to claims over his personal conduct.
The Metropolitan Police said on Tuesday it had launched an investigation in December 2016 "following a referral from another police force" relating to "allegations of serious sexual offences against a teenage boy".
The alleged offences are said to have taken place between 1997 and 2000.
"As part of these enquiries, a man who was in his 40s at the time of the interview, was questioned by police under caution in July 2018," the Met added.
It said the Crown Prosecution Service ultimately decided "the evidential threshold had not been met to bring charges" and the case was closed in May 2019.
The police investigation into the allegations were first reported by The Mirror.
Mills, who has not yet commented on his sacking, was taken off air by the BBC last Tuesday.
The 53-year-old signed off that show saying "back tomorrow" - but Gary Davies presented Wednesday's show.
Mills took over from Zoe Ball on Radio 2's breakfast show in 2025 after a long career at the BBC and regional radio.
He was paid between £355,000 and £359,999.
His sacking is the latest in a series of controversies to befall the BBC in recent years and comes a week after it announced Matt Brittin would be its new director-general in May.
In an internal email on Monday, Lorna Clarke, the BBC's director of music, wrote: "I know that this news will be sudden and unexpected and therefore must come as a shock.
"Not least as so many of us have worked with Scott over a great many years, across a broad range of our programmes on R1, 5Live, R2 and TV.
"I felt it was important to share this news with you at the earliest opportunity.
"Of course, it will also come as a shock to our audience and loyal breakfast show listeners too.
"I will update everyone with more information on plans for the show when I'm able to. While I appreciate many of you will have questions, I hope you can understand that I am not going to be saying anything further now."
Kayla Smith, 18, and Archie Rycroft, 19, have been remanded in custody to appear before Leeds Magistrates' Court on Tuesday, alongside a 17-year-old boy who cannot be named for legal reasons.
Chloe died in hospital after being found unconscious with stab wounds in Leeds at 5.55am on Saturday.
Another 18-year-old man from the city has been arrested on suspicion of murder and remains in custody.
An 18-year-old woman and a 17-year-old boy, who were arrested on suspicion of murder, have been released on bail pending further enquiries.
Police were called to an address in Kennerleigh Avenue, in the Austhorpe area, east of Leeds city centre, on Saturday morning following reports that a young woman had been found unconscious.
Flowers have been left at the scene for the teenager.
Chloe's mother said in a statement following her death: "My beautiful princess Chloe. I cannot put into words how I feel that you are not here with me.
"You are my life, my world, my best friend and I know that I am yours. I cannot live without you - I need you.
"You are stunning, confident, loyal, honest and my family-oriented princess."
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The statement continued: "When you walk into any room, it lights up with your bubbly personality. There is so much I could say. There's a big hole in my heart that can never be filled.
"Your two sisters and big brother will always love and miss you to infinity. You will always and forever be in our hearts. Love Mum, Connor, Courtney and Cienna."
Baroness Anne Longfield, the former children's commissioner, made the promise in her first statement since being appointed to run the statutory independent inquiry last December.
In it, she makes clear the inquiry will focus on sexual exploitation by grooming gangs, not other forms of sexual abuse such as individual, familial or institutional.
The inquiry will examine institutions such as police forces and local authorities that failed to protect children and whether "the ethnicity, culture, or religion of either perpetrators or victims influenced patterns of offending, and whether these factors shaped the institutional response".
In what seems like a criticism of previous investigations, the inquiry team said: "These are questions that previous reviews chose not to address. This inquiry will not avoid them."
Baroness Longfield added: "Children across England and Wales were - and still are - sexually abused and exploited by grooming gangs. Raped. Trafficked. Threatened into silence.
"That is not disputed. What has been disputed, what has been minimised, explained away, or buried for far too long, is why the institutions that exist to protect them so often chose not to act."
The inquiry, which is expected to have offices in London, Leeds and Wales, will finish its work by March 2028 with a budget of £65m.
There are several headwinds the inquiry team is trying to face down: the fact the chair is not a judge; the previous squeamishness of others about ethnicity; and an overriding sense from survivors, who've already been badly failed by the state, that this will be another whitewash.
Over the last three months, the team has been meeting dozens of victims and survivors experiencing this scepticism and questions about whether it will make a difference.
This, they said, has helped determine the terms of reference, and the team has offered reassurance and promised to publish as they go so that institutions under investigation will have the evidence exposed when found. There is also a pledge to look back over 30 years - beginning in 1996.
It has promised to investigate how grooming gangs operated and were able to do so for so long, what police forces, social services, local authorities and schools knew, and what they did or didn't do.
While Baroness Longfield is not a judge, she will use some of her budget to employ legal assistance, and the Inquiry will have statutory powers which can force reluctant witnesses to give evidence.
There is an emphasis on the experience of the Baroness and her two panel members: Zoë Billingham, who has spent much of her career inspecting public services and Eleanor Kelly, the former Southwark chief executive who oversaw the response to the Grenfell disaster.
Baroness Longfield said: "Together, we bring decades of experience in protecting and promoting the interests of children, holding police forces and institutions to account, safeguarding vulnerable women and girls from violence and abuse, and providing strong local leadership in times of crisis."
Alongside the national inquiry, there will be an unspecified number of local inquiries, each with a £5m budget. One will be in Oldham, and there has been local pressure for one in Bradford.
It was January last year when the government came under political pressure for this inquiry after a series of tweets by Elon Musk about grooming gangs in the UK. The prime minister ordered a rapid national audit but initially resisted a full national Inquiry.
Then, in June, Louise Casey's audit found "ignorance, prejudice, and defensiveness contributed to a collective failure to protect children" and that data collection on ethnicity was flawed.
At this point, the government promised a full national statutory inquiry.
It took until October for two candidates for chair to be mooted, but both withdrew after a poor reaction from survivors, many of whom wanted a judge to lead it. Then, in December, Baroness Longfield was appointed.
In recent days, Conservative MP Robbie Moore has expressed concern that evidence may have been destroyed because of the length of time it took for the government to instruct institutions to preserve records.
A Home Office spokesperson said: "Since Baroness Casey's National Audit, we have worked across government to ensure records relevant to the draft Terms of Reference are appropriately retained by public sector organisations."
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Home Secretary Shabana Mahmood said: "The grooming gangs scandal is one of the darkest moments in our country's history, where the most vulnerable people were abused and exploited at the hands of evil child rapists.
"The chair and I have agreed that the Inquiry will be laser-focused on grooming gangs and will explicitly examine the role of ethnicity, religion and culture of the offenders and in the response of institutions.
"There will be no hiding place for the predatory monsters who committed these vile crimes."
The inquiry is due to begin its investigation on 13 April.
The body of Donna Keogh, who was last seen in Middlesbrough town centre on 28 April 1998, has never been found.
Cleveland Police arrested a 64-year-old man in Leeds on Tuesday, on suspicion of her murder.
Donna was known to have travelled to Leeds in 1998 and police have been carrying out inquiries in the city in recent weeks.
Senior investigating officer Detective Chief Inspector Steven Chatterton said: "This morning we have made an arrest as a result of our recent inquiries, and the man remains in police custody at this time for questioning.
"I would like to reiterate our appeal for anyone to contact us who may have seen Donna, spoken to her, or knows anything about her movements in Leeds in 1998 to come forward.
"We are in close contact with Donna's family, and they have lived with unbearable uncertainty for nearly 30 years. We are determined to find out what happened to Donna for them.
"Somebody out there knows the truth. If you have information, please tell us. You can contact us directly or report anonymously."
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The charity Crimestoppers has offered a £20,000 reward for information about Donna's murder.
In 2018, police found human remains after digging up an allotment on Teesside, but forensic testing revealed they dated back to medieval times.
The UK, Germany, France and Italy said the move was "de facto discriminatory" and "Israel risks undermining its commitments to democratic principles".
A joint statement called the death penalty "an inhumane and degrading form of punishment without any deterrent effect".
UK Foreign Secretary Yvette Cooper posted the statement on X, adding: "The death penalty is wrong and we oppose it around the world."
Israel's far-right national security minister, Itamar Ben-Gvir, who wore noose-shaped lapel pins in the run-up to the vote, has campaigned for tougher punishments for Palestinians convicted of nationalistic offences against Israelis.
"We have made history," Mr Ben-Gvir said, in a post on X. "Any terrorist who goes out to kill should know - he will be sent to the gallows".
He was also scathing about criticism from the European Union, adding: "We are not afraid, we do not yield".
The Palestinian ministry of foreign affairs said the law "constitutes a decision to carry out institutionalised extrajudicial killings according to racist standards".
"The ministry affirms that Israel has no sovereignty over Palestinian land and that Israeli laws do not apply to the Palestinian people," it added.
Opponents of the bill, under which executions should be carried out within 90 days of sentencing, said it was racist, draconian and unlikely to deter attacks by Palestinian militants.
Critics include Israelis and Palestinians, international rights groups and the UN, some of whom fear the death penalty could be applied solely to Palestinians convicted of murdering Jewish citizens of Israel.
The sentence will be applied by a military court to anyone convicted of murdering an Israeli "as an act of terror".
Such courts try only West Bank Palestinians, who are not Israeli citizens. The bill says military courts can change the penalty to life imprisonment in "special circumstances".
Israel's courts, which try Israeli citizens, including Palestinian citizens of Israel, can choose between life imprisonment or the death penalty in cases of murder aiming to harm Israeli citizens and residents or "with the intent of rejecting the existence of the state of Israel".
'Discriminatory by design'
Amichai Cohen, a senior fellow at the Israel Democracy Institute's Centre for Democratic Values and Institutions, said the distinction is discriminatory as it means, in effect, Jews "will not be indicted under this law".
In addition, the West Bank is not sovereign Israeli territory, so under international law, Israel's parliament should not be legislating over it, Mr Cohen said.
The Association of Civil Rights in Israel said it had petitioned the country's highest court to challenge the law, calling it "discriminatory by design" and "enacted without legal authority" over West Bank Palestinians.
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Israel has the death penalty on its books, but the country hasn't put anyone to death since Nazi war criminal Adolf Eichmann in 1962.
The bill will not apply retroactively to any of the militants Israel currently holds who attacked the country on 7 October 2023.