Princess Diana's brother makes new explosive claims against King Charles in upcoming book

Princess Diana's brother has unleashed a string of criticism against King Charles III in his new book, alleging the monarch was "giddily elated" the night his ex-wife died in a car crash, as Buckingham Palace issued a rare rebuke of the startling claims.

Charles Spencer wrote that the then-prince "sounded giddily elated – like a lottery winner" on the night Diana died three decades ago, in the latest extract of his book published by the Daily Mail on Thursday (Sep 17).

In another extract released earlier, Spencer claims that days after her death, the future king told him: "Rest assured, we'll forget her soon enough."

Buckingham Palace took the unusual step of strongly pushing back against the allegations earlier Thursday, with UK newspapers splashing the war of words between Spencer and the king, who was married to Diana for 15 years.

"His Majesty is mindful that the pain of fraternal grief can cloud reason, affect judgement and colour memory in ways others do not recognise, even many years after such a loss," a palace spokesperson said, adding that they do not normally comment on books.

Spencer's book, titled Swan Song: Diana, My Sister and set to be published next week, is being serialised in the Daily Mail.

In the latest extracts, Spencer claims "there were others in the Palace, I already knew, who were relieved – indeed, pleased – that she had gone".

He also alleges Charles subjected him to a "stream of anger" after he insisted Diana would not have wanted her sons, princes William and Harry, then aged 15 and 12, to walk in her funeral procession.

"He 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!'," Spencer writes.

Diana, who was hugely popular in the UK, died in Paris aged 36 after the car she was travelling in crashed as the driver tried to get away from paparazzi photographers.

Her death sparked an outpouring of grief in Britain and led to accusations that the monarchy failed to show the appropriate empathy.

Both heir-to-the-throne William and his brother Harry, who quit royal duties in 2020 but has just returned to Britain, have spoken previously about how difficult it was to walk behind her coffin.

'RECOLLECTIONS MAY VARY'

Julian Payne, who was communications secretary to Charles on the 20th anniversary of Diana's death in 2017, said he found it hard to believe his former boss had said what Spencer claims he did.

"It's just not language that I recognise," he told the BBC. 

Royal watchers said Buckingham Palace's quick response to Spencer's allegation hinted at the anger felt within the monarchy at the claim.

"Sometimes the palace have to weigh up whether or not they want to just leave things and adopt the never complain, never explain mantra," Sunday Times royal editor Roya Nikkhah told the BBC.

"But I don't think that would have washed in this scenario.

"It's too big a claim. And they know with the serialisation there are days more of this kind of stuff coming and so they'll be braced."

UK media also likened the language in the palace's statement to the late Queen Elizabeth II's response in 2021 to claims of racism in the royal family from Harry and his wife Meghan.

At the time, the queen said that "some recollections may vary".

Charles and Diana's tumultuous marriage between 1981 and 1996 was regularly featured in British newspapers and continues to fascinate.

Diana's famous "revenge dress" that she wore on the evening in 1994 when Charles made a public admission of adultery is to be auctioned in New York in December.