LONDON, United Kingdom (AFP)—Charles Spencer’s book about his late sister Princess Diana, packed with explosive revelations concerning King Charles III that have rocked Britain’s monarchy in recent days, went on sale Tuesday.

“Swan Song: Diana, My Sister”, a memoir written by Diana’s younger brother, has been published by Penguin in various English-speaking countries and translated into 12 languages for wider release.

Billed as chronicling her life from his perspective, Spencer’s 384-page book comes almost three decades after Diana was killed in a 1997 car crash in Paris.

Extracts serialised in the British tabloid the Daily Mail last week have triggered sensational headlines around revelations involving her ex-husband, and now King Charles III.

Charles issued a rare rebuttal after Spencer wrote that the then Prince of Wales told him in a phone call shortly after Diana’s death: “Rest assured, we’ll forget her soon enough.”

Spencer also claimed Charles had “sounded giddily elated, like a lottery winner” at the news of her demise.

“I’m looking forward to reading it,” self-described Diana fan Mary Scheible, 69, from the United States, told AFP as she bought a copy from a bookshop while visiting London.

“What I’ve seen are sentences taken maybe out of context. So I want to read the book to get the full story and then make my opinion.”

Spencer, 62, who has worked as a US television journalist, has said he wrote the memoir to correct “untruths that have become accepted over time”.

“Diana would be cheering from the rafters at this book,” he told the Mail on Sunday.

– ‘Gaslit’ –

English copies went on sale in countries including Britain, the US, Canada and Australia, with other countries such as Germany, Brazil and Spain getting translated versions.

Despite the recent publicity, the book only sat in 12th in Amazon UK’s non-fiction bestseller list Tuesday.

Diana’s death, aged just 36, sparked an outpouring of grief in Britain and beyond for the woman dubbed “the people’s princess”.

And it triggered accusations that the then monarch, Queen Elizabeth II, failed to respond swiftly with empathy and understanding.

Spencer told the BBC that Charles “went ballistic” after he insisted Diana would not have wanted her sons, princes William and Harry, to walk behind her coffin in her funeral procession. They were then aged 15 and 12, respectively.

A Buckingham Palace spokesperson last week issued a rare reaction from the 77-year-old king.

“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,” it stated.

But Spencer insisted in the BBC interview that “those are exactly the words he said,” adding: “I don’t hear (Charles) saying he didn’t say that.”

And he criticised the palace’s reaction, telling The Mail on Sunday: “It is not every day you wake up to find you’ve been gaslit by the king.”

Spencer also reveals Diana had at times contemplated suicide during her tumultuous 1981-1996 marriage to Charles.

He detailed how she once drove down to a notorious clifftop in southern England where people used to deliberately fall to their deaths but that her love for her sons “stopped her from going further”.

– ‘Improbable’ –

After Diana’s death, Charles later married his long-time mistress, Camilla Parker Bowles, who is now the queen.

In another shocking claim, Spencer wrote Diana had felt “revulsion” for Mohamed Al-Fayed, the father of her boyfriend Dodi Fayed, who was also killed in the Paris crash.

He alleged she claimed the late Harrods owner — who has been accused of large-scale rape and other sexual abuse — had groped her and made sexually suggestive comments.

Royal experts have questioned some of the book’s claims.

Royal biographer Robert Hardman wrote on X that he witnessed Charles, rather than elated, “distraught and in tears” at Diana’s funeral.

Andrew Morton, author of the 1992 book “Diana: Her True Story,” in a comment in The Times wrote that Spencer’s claims about the phone call with Charles were “incendiary and disputed”.

Royal commentator Jennie Bond told the BBC the memoir was “vindictive”.

Spencer inherited the family’s stately home Althorp, where he and Diana grew up. She is buried on an island in the grounds.

After her death, he accused the media of having “blood on their hands” and in his raw eulogy at Diana’s funeral, vowed to always look out for her two sons.