Princess Diana’s brother has made explosive claims that her former husband, the then Prince of Wales, sounded “giddily elated … like a lottery winner” on the night she died in a car crash in 1997.

In a new excerpt from the book Swan Song: Diana, My Sister, Charles Spencer said the prince rang him and “sounded strangely matter-of-fact”.

The bombshell extract was published by Britain’s Daily Mail on Thursday (UK time).

“Unlike my other callers, who were stunned, barely able to articulate their condolences and offers of help, he sounded giddily elated — like a lottery winner, I remember thinking at the time,” one passage read.

“He let me know he had informed [Princes] William and Harry of their mother’s death, first thing that morning, in their bedrooms at Balmoral.

“It all sounded strangely matter-of-fact, given the enormity of the disaster.

“Looking back now, I suspect the prince’s first reaction must have been to think more of how this event might free him to marry the woman he loved, rather than appreciating the loss of one he did not.”

Then Prince Charles with his wife Princess Diana on an Australian visit in 1985. Photo: AAP

Diana died at the age of 36 when the car carrying her and her lover Dodi al-Fayed crashed in Paris as it sped away from chasing paparazzi photographers on ‌motorbikes.

Further shocking revelations in Thursday’s release included that Diana had contemplated ending her life several times.

“It is a sad fact that, in her later years, Diana drove herself more than once to Beachy Head, the highest chalk sea cliff in England, while contemplating ending it all. Her love for her sons stopped her from going further,” her brother’s book states.

Earl Spencer writes that he believed the prince may have contributed to Diana’s eating disorder, revealing that Charles squeezed her waist during their engagement and said: “Oh, a bit chubby here, aren’t we?”

His book also says Diana confided in a friend that the prince told her he did not love her, but was happy to marry her.

The book will be released next week.

The latest extracts continue a war of words with Buckingham Palace after it hit back at earlier claims in the memoir with a short statement, saying “the pain of fraternal grief can cloud reason”.

“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,” a palace spokesman said after the first excerpts were published on Wednesday.

It is a rare public statement from the palace, which is famously known for a doctrine – adopted under the late Queen Elizabeth II – of “never complain, never explain”.

‘We’ll forget her’

The excerpt from Wednesday claimed Spencer had a heated conversation with the prince in the hours after Diana died.

He alleges the now-King at one point said “we’ll forget her soon enough”.

Spencer ⁠claims the comments were made in an argument over whether William and Harry – then 15 and 12 – should walk ⁠behind their mother’s coffin during her funeral.

Spencer claims he told the King that Diana wouldn’t have wanted her sons to go through something so traumatic, so publicly.

According to the upcoming book, the King said he wanted his sons to be involved in the funeral procession. He said he’d made the same walk in the procession of Lord Mountbatten 18 years earlier and said it wasan example of what he wanted his sons to follow.

Spencer said he pointed out that the King was 30 when Mountbatten died. He said the King “went nuts”.

“Prince Charles continued his stream of anger, without me interrupting. Then he stopped,” Spencer writes in Swan Song.

“I assumed the pause signalled an effort to bring himself under control, but then 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 that he was “so stunned” by the alleged remarks that he took a few seconds before replying: “I can’t believe you just said that.”

Diana became the most photographed woman in the ​world after marrying ‌the then Prince of Wales in a glittering ceremony in 1981. However, the marriage turned sour ​and the couple eventually divorced in 1996.

Prior to the book’s release, Spencer said: “The aim of this book is to tell the truth about Diana ​from her brother’s perspective … I want to speak on Diana’s behalf and ​do so in an ⁠openly positive way.”

Swan Song: Diana, My Sister will be published next week. It is expected to be highly critical of the royal family.

-with AAP