Earl Spencer has accused King Charles of gaslighting him and being "astonishingly provocative" in the latest escalation of his row with the royals.
The earl has made a series of damning claims about the King in a new memoir - alleging he said "we'll forget her soon enough" during a supposed row over funeral arrangements for his sister Princess Diana.
Buckingham Palace afterwards said in a statement that "fraternal grief can cloud reason, affect judgment and colour memory in ways others do not recognise".
However, the earl has stood by his comments in multiple interviews - where he's also likened the media's treatment of Prince Harry and Meghan to what his late sister went through.
He told The Mail on Sunday: "It is not every day you wake up to find you've been gaslit by the King.
"It was astonishingly provocative and below the belt because it was essentially trying to say I'd lied without the King being able to deny what I'd said.
"I also thought it was a rather poor imitation of the 'recollections may vary' quote, which was a much more elegant way of putting things, but in these circumstances entirely out of place."
He also said that "Diana would be cheering from the rafters at this book".
The earl made the allegations in Swan Song: Diana, My Sister, which is being serialised in the Daily Mail and is due to be published next week.
Earl likens Sussexes' 'unpleasant' treatment to Diana
In another interview released on Sunday, the earl was asked if he thought Diana would "identify" with how her youngest son Harry and his wife, Meghan, have been treated by the media.
"If you look at an article in a tabloid about Diana or the couple that you were mentioning, Harry and Meghan, you know, they can be really, really unpleasant," he told the BBC.
"And I think it would be really beholden on people to learn from Diana's example."
The earl added: "I'm not here to speak for Harry and Meghan, but for anyone who's being destroyed in this way daily, it must be such a cancerous influence in their life."
The Duke of Sussex has been highly critical of the media scrutiny he and Meghan have faced, and blamed a tabloid newspaper for a miscarriage his wife suffered in 2020.
In a separate BBC interview earlier this week, the earl insisted he is "telling the truth" about Charles.
He said: "I told friends and family straight away, close friends and family, about what had been said, because it was so monstrous."
The King allegedly made the remarks about forgetting Diana during an argument over whether the then Prince William and Prince Harry should follow the princess's funeral cortege.
Earl Spencer walked behind Diana's coffin during the funeral procession in 1997 alongside Harry, William, then-Prince Charles, and the late Duke of Edinburgh.
In the latest extract of the book serialised in the Daily Mail, he described the train journey from London to Althorp after the funeral.
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The earl wrote: "My chief memory of that train journey is of being concerned at the lack of obvious care for Harry, as he decompressed from the ghastliness of the morning.
"He needed Diana's hugs, of course, and they would forever be denied him.
"But instead of calm and nurture, he was allowed to spin out of control."
Despite the string of damning claims, the Royal Family have been carrying on with business as usual.
On Saturday, the Queen was welcomed with applause to Chatsworth House in Derbyshire for the first day of the festival for The Queen's Reading Room, a charity she founded following the success of her Instagram book club during the pandemic.
Camilla spoke of her love for books that have a "life-enhancing power" and said being at Chatsworth House, which has a library of over 17,000 books, was "like coming home".
(c) Sky News 2026: Earl Spencer accuses King of gaslighting him – and says press treatment of the Sussexes 'ec
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