Buckingham Palace is in a war of words with Earl Spencer, the brother of Diana, Princess of Wales, over a controversial memoir about her life and death.

King Charles is accused of insensitively saying to Earl Spencer, in the wake of Diana’s death in 1997, that “we’ll forget her soon enough”, according to excerpts published in the Daily Mail.

But the Palace has pushed back unusually strongly, angered by the claims and attempting to cast doubt on them.

“While we do not comment on books as a matter of principle, His Majesty is mindful that the pain of fraternal grief can cloud reason, affect judgment and colour memory in ways others do not recognise, even many years after such a loss,” it said.

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 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 Diana’s sudden death. And this book will give an insider’s view on those events.

In the published excerpt, Earl Spencer claims 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’s a claim that’s 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.

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 is set to intervene in the debate about artificial intelligence, calling on AI industry leaders to prevent it becoming a destructive force.

“Those in our world who value our humanity and its vital moral component are anxiously seeking your reassurance that we will not lose control of our destiny,” the King is expected to say on Thursday, as he hosts a gathering of leading AI firms at an Dumfries House, in Ayrshire.

“The development of AI, its substance and its pace, are both intriguing and deeply concerning in equal measure,” the King will say.

The rapidly-advancing technology has raised fears about its safety, as well as a threat to jobs.

The King will be joined by AI minister Kanishka Narayan and representatives of tech firms such as OpenAI, Anthropic, Nvidia and Google DeepMind.

He will ask the question about how the benefits of AI can be harnessed while still ensuring that it remains safe, and raise the issue of whether there can be international co-operation in protecting it from being misused.

“The decisions taken at this formative time will shape the world inherited by future generations,” he will say. “And so, the task before you is not merely to advance technology, but to ensure that it remains firmly in the service of humanity, community and the natural world.”

Meanwhile, during the day, Prince William and Catherine will visit community and volunteering projects on the Isle of Bute.

The couple – who are called the Duke and Duchess of Rothesay in Scotland, rather than the Prince and Princess of Wales – will make their first official visit to the town of Rothesay.

They will see the traditional sport of shinty, visit a community-owned pub and hear about those working to protect the island’s natural environment.

Later, Prince Harry will hold his first big public event since returning to the UK, when he appears at the inaugural Invictus awards ceremony.

This will celebrate the “resilience, service and unconquered spirit” of those involved in the sports events for injured service personnel.

It’s not yet known whether he will be accompanied by his wife, Meghan.

It is unusual to have so many royal events at the same time, but it could be a sign of things to come, with Prince Harry and Meghan back in the UK and running their own programme of engagements.

A letter, sent on behalf of the King last week, made clear that the Sussexes are not carrying out royal engagements, but even as “private citizens” they are likely to get plenty of press attention for their visits.

The controversy over the letter suggested some tension in their return and raised questions about how they will fit into wider royal arrangements.

Harry and Meghan have already been in the headlines this week over switching schools for their children, after security fears over the school run.

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