The language is reminiscent of Queen Elizabeth's unexpectedly firm response to claims of racism by the Duke and Duchess of Sussex in 2021, with the comment that "recollections may vary".

And the row threatens to overshadow a very crowded day for the royals - with the King, Prince William and Catherine attending events, and Prince Harry making his first big appearance since returning to the UK.

Earl Spencer's book, Swan Song: Diana, My Sister, to be published next week, seems set to reopen a very difficult time in the recent history of the Royal Family - written from the perspective of her own Spencer family.

The death of Princess Diana, a hugely popular figure, had created a volatile atmosphere, in which the royals were accused of failing to show feeling and empathy, and had seemed out of touch with the public mood.

Earl Spencer's emotional and defiant speech at her funeral added to that cloud of grievance hanging over Princess Diana's sudden death. And this book will give an insider's view on those events.

In the published excerpt, Earl Spencer says the then-Prince of Wales subjected him to a "stream of anger" after he insisted Diana would not have wanted Princes William and Harry, then aged 15 and 12, to have to walk in her funeral procession.

Earl Spencer wrote in the book: "He [Charles] unleashed down the phone what I have always taken to be his pent-up contempt for Diana, and his horror that the world was so bowled over by her death. 'Rest assured,' he hissed, 'we'll forget her soon enough'."

It is a claim that is being rejected by the Palace, who see it as being entirely out of character for a man with a deeply compassionate nature, who at the time was dealing with his own grief and that of their two sons.

Prince Harry has previously said that walking behind his mother's coffin aged 12 was something no child "should be asked to do".

In 2017, he told the BBC he did not "have an opinion whether that was right or wrong" but. "looking back on it", he was glad to have been part of the day.

Earlier on Wednesday, it emerged that copies of Earl Spencer's unreleased book had been stolen from a lorry in the Netherlands.

Julian Payne, the monarch's former communications secretary, told the BBC that the King's apparent comments in the book were "just not language that I recognise".

He said the "highly unusual" statement from the Palace demonstrated the "strength of feeling that there must have been for them to feel that they needed to go out there and correct it".

The dispute comes when multiple royal events will be jostling for attention.

King Charles intervened in the debate about artificial intelligence on Thursday, calling on AI industry leaders to prevent it becoming a destructive force and warning of the potential "existential dangers" it could pose.

"Those who have created these technologies are now increasingly warning that AI risks developing darker capacities - perhaps even to take life," the King said as he hosted a gathering of leading AI firms at Dumfries House, in Ayrshire.

"In this regard, if I may say so, there seems urgency in adequately considering the existential dangers of such technologies falling into the wrong hands, and being used in potentially catastrophic ways."

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