Prosecutors said Sharaz Ali, 40, was "motivated by jealousy and fuelled by drink and drugs" when he set fire to Bryonie Gawith's home early on 21 August last year.
Jurors heard that Ali went to the home in Westbury Road, Bradford, aiming to "take revenge" on his ex, Antonia Gawith, who was staying there after ending their "abusive" seven-year relationship earlier that month.
Antonia Gawith managed to escape, but Bryonie Gawith, 29, and her children Denisty Birtle, nine, Oscar Birtle, five, and 22-month-old Aubree Birtle died in the blaze.
Ali told a jury he had no intention of harming others when the house went up in flames, saying: "I didn't want to hurt anyone but myself."
But after a trial at Doncaster Crown Court, he was found guilty of four counts of murder and attempting to murder Antonia Gawith.
Calum Sunderland, 26, who went with Ali to the house and kicked the door in for him, was found guilty of the manslaughter of Bryonie Gawith and her three children, but cleared of the more serious charges of murder.
He was also cleared of attempted murder, and an alternative count of attempting to cause grievous bodily harm, in relation to Antonia Gawith.
Mohammed Shabir, 45, who had also been due to go on trial, died of a heart attack in October after collapsing in prison.
Reading a statement on behalf of her family outside court, Antonia Gawith said her sister, nieces and nephew's futures have been "stolen".
"Even with justice, nothing will ever make this right," she said.
"Nothing will ever fill the silence where their laughter should be. Nothing will ever bring back our family.
"We will forever carry this brokenness, and yet we will hold on to them tightly in only ways we can now, through our memories, our photos and our precious videos. Those are all we have left now."
After the verdicts, the judge, Mr Justice Hilliard, thanked jurors and said the case had been "distressing beyond measure - three children and their mother murdered".
"I don't think anyone who heard Antonia's desperate cries for help will ever forget them," he said.
"These are truly dreadful crimes."
The judge also praised the "extraordinary bravery" of those who tried to save the children trapped in the house.
Ali and Sunderland, a convicted arsonist, were driven to the house by Shabir, stopping on the way to fill a seven-litre canister with petrol, the court heard.
Doorbell footage captured Ali telling Sunderland, who was carrying the petrol and a lighter, to "kick the door in", which he did before running back to the car.
Antonia Gawith said she saw an "angry" Ali run into the house and begin pouring petrol on her while shouting before setting himself and the house on fire.
'I couldn't save them'
In a video interview played to jurors, she sobbed as she told police how she "couldn't save" her sister, nieces and nephew, as she tried frantically to get back in the house through the back door.
"I was just screaming, trying to get back in the house and I couldn't get in. I couldn't save them," she said.
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West Yorkshire Police's Detective Chief Inspector Stacey Atkinson said: "Bryonie and her three children would still be alive today if it wasn't for the horrific and truly callous actions of Ali and Sunderland that day.
"They left a mum and her three children completely helpless whilst her sister and their auntie watched on in horror.
"Our thoughts and sympathies are with the family, who despite their immense strength of character now face the rest of their lives without them."
Senior Crown Prosecution Service prosecutor Amanda McInnes said Ali was a "selfish killer who had no regard for anyone but himself".
"He was motivated by jealousy and his actions have now needlessly robbed a family of their loved ones," she said.
"Both men played their role and caused the deaths of a young family who should still be with us today."
The writer, whose real name was Madeleine Sophie Wickham, revealed last year she had been diagnosed with an aggressive form of brain cancer in 2022.
A statement posted to her Instagram account read: "We are heartbroken to announce the passing this morning of our beloved Sophie (aka Maddy, aka Mummy). She died peacefully, with her final days filled with her true loves: family and music and warmth and Christmas and joy.
"We can't imagine what life will be like without her radiance and love of life.
"Despite her illness, which she bore with unimaginable courage, Sophie counted herself truly blessed - to have such wonderful family and friends, and to have had the extraordinary success of her writing career. She took nothing for granted and was forever grateful for the love she received.
"She will be missed so much our hearts are breaking."
Kinsella's novels have sold more than 45 million copies in more than 60 countries, and have been translated into more than 40 languages.
In April 2024, she revealed she had been diagnosed with an aggressive form of brain cancer in 2022.
In a post on social media, Kinsella said she had been receiving chemotherapy and radiotherapy at London's University College Hospital, and had undergone "successful" surgery.
She said she "wanted for a long time to share with you a health update and I've been waiting for the strength to do so".
"At the end of 2022 I was diagnosed with glioblastoma, a form of aggressive brain cancer," she said.
"I did not share this before because I wanted to make sure that my children were able to hear and process the news in privacy and adapt to our 'new normal'.
"At the moment all is stable and I am feeling generally very well, though I get very tired and my memory is even worse than it was before!
"I am so grateful to my family and close friends who have been an incredible support to me, and to the wonderful doctors and nurses who have treated me."
Kinsella's most recent book is What Does it Feel Like?, published in October 2024 and which "is fiction, but it is my most autobiographical work to date", the author wrote on her website.
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Other books by the London-born author include The Burnout, released in October 2023, Can You Keep A Secret? and The Undomestic Goddess.
The first two novels in her hit eight-book Shopaholic series, The Secret Dreamworld Of A Shopaholic and Shopaholic Abroad, were adapted into the 2009 film Confessions Of A Shopaholic, starring Isla Fisher.
She is survived by her children, four sons and a daughter, and her husband Henry Wickham.
Bill Scott-Kerr, publisher at Transworld, the publishing home of Kinsella for the past 30 years, said: "She has been such an unshakeable pillar of our publishing at Transworld for so many years that the thought of a year without a Sophie Kinsella to publish is inconceivable."
He added: "Maddy leaves behind a glorious and indelible legacy: a unique voice, an unquenchable spirit, a goodness of intent and a body of work that will continue to inspire us to reach higher and be better, just like so many of her characters.
"On a personal level Maddy was the embodiment of joy, an extraordinarily clever, funny, sassy, impish, kind and generous collaborator who brought light into our lives. She was as part of this company as anyone, and we will all truly miss her."
At a harbourside park in Sydney, teenagers told Sky News they've found a way around the ban by using VPNs or their parents' social media accounts.
I met a dozen teenagers in the suburb of Balmain, and almost all of them were still accessing social media.
Felix Webster is 14 and is still using his social media accounts despite the ban: "I think it's just being slow and it's going to block everyone within the next week."
However, Felix says "everyone's going to find a way around it easily".
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Kira Solanki, 14, wants to "wind down" after school and says social media is a way to "take a break, but now [I] can't do that any more".
Australia's law to restrict 10 social media apps (so far) to kids aged under 16 is an extraordinary move by a government determined to try to stamp out cyberbullying and online addiction.
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Raphael Williams Veazey argues kids can still be bullied in real life.
"I think it's a bit stupid," Raphael says. "They could have used different measures, instead of an outright ban for everyone."
He also explains that he tricked his social media platform into thinking he was older.
Australia's restrictions still allow children to use messaging services like WhatsApp, but TikTok, Instagram and Snapchat are all banned.
With summer school holidays barely a week away, 14-year-old Kobe Staunton expects it could be a quiet one.
"It'll be pretty like lonely and boring, because I can't speak to my friends on most of the apps."
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Some parents are also concerned about whether the ban will really work. Children can still look at social media apps, like YouTube, even if they don't have an account.
Ryan Alridge says, "There's a lot of good stuff [in the law] but it's not necessarily going to suddenly save all the kids from harm."
Australians are dealing with a brave new world of social media rules, but it's still unknown whether this nationwide social experiment will be enough to get children off their devices and outdoors.
The disaster in Fez unfolded while one building was hosting an Aqiqah, a traditional Muslim celebration marking the birth of a child.
This building was home to eight families, the local authorities said, while the other was unoccupied.
A survivor, who lost his wife and three children in the overnight collapse, told a local TV station that rescuers had only been able to retrieve one body.
Another survivor, interviewed by SNRT News, Morocco's national broadcaster, said: "My son who lives upstairs told me the building is coming down."
She added: "When we went out, we saw the building collapsing."
Witnesses said the buildings had shown signs of cracking for some time, when interviewed at the scene by SRNT.
Both buildings, in the Al-Mustaqbal neighbourhood, were four-storeys high.
Announcing an investigation, the Fez prosecutor said 16 people had also been injured, citing preliminary figures.
Some 38,800 buildings across the country are classified as being at risk of collapse, according to Adib Ben Ibrahim, housing secretary of state.
The latest collapse is one of the worst in Morocco since a minaret fell in the historic northern city of Meknes, killing 41 people in 2010.
Fez, a former Moroccan capital, is the country's third most-populous city, as well as one of its oldest, dating back to the eighth century.
But deteriorating living conditions, and poor public services, sparked a wave of anti-government protests there, and in other cities, two months ago.
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The unrest, which was driven by younger Moroccans, revealed deep-seated anger over poverty and public services.
It comes at a time when the government is pushing ahead with ambitious infrastructure projects, including modern stadiums, ahead of the 2030 FIFA World Cup.
Fez, one of the host cities, has some of the country's poorest neighbourhoods.
Seattle's PrideFest 2026, which organisers say regularly sees more than 200,000 participants, takes place on 27 and 28 June - immediately following the match.
Local organisers have said the 26 June game at the Seattle Stadium will include a "once-in-a-lifetime moment to showcase and celebrate LGBTQIA+ communities in Washington".
In Iran, where gay couples can face the death penalty, the president of Iran's Football Federation, Mehdi Taj, condemned the decision to use Seattle as a venue and the timing of the match.
Mr Taj told Iranian state TV: "Both Egypt and we have objected, because this is an unreasonable and illogical move that essentially signals support for a particular group, and we must definitely address this point."
He said Iran would bring up the issue at a FIFA Council meeting in Qatar next week.
The football federation in Egypt, where Human Rights Watch says people from LGBTQ+ communities face persecution, said in a statement that it had written to FIFA "categorically rejecting any activities related to supporting homosexuality during the match between the Egyptian national team and Iran."
The letter also stated: "Information had circulated indicating the local organising committee's decision and plans to hold some activities related to supporting homosexuality during that match" and the federation "completely rejects such activities, which directly contradict the cultural, religious and social values in the region, especially in Arab and Islamic societies".
In Seattle, the local organising committee said it was "moving forward as planned with our community programming outside the stadium during Pride weekend and throughout the tournament," having already promoted an art contest ahead of the match.
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It added: "We get to show the world that in Seattle, everyone is welcome."
Seattle PrideFest has been organised in the city since 2007 by a nonprofit group which designated the 26 June match for celebration before FIFA carried out the World Cup draw on Friday.
On Saturday, FIFA announced the Egypt-Iran game had been allocated to Seattle instead of Vancouver, where the teams' group rivals Belgium and New Zealand will play at the same time.
FIFA has been asked for a comment.