A book published Tuesday by the brother of the late Princess Diana has made headlines around the world with its damning allegations about Diana's ex-husband, now King Charles III, and reopened decades-old wounds within Britain's royal family.

In "Swan Song: Diana, My Sister," Charles Spencer alleges that he argued with the then-Prince Charles over palace plans for Prince William and Prince Harry, then 15 and 12, to walk behind their mother's coffin during her 1997 funeral procession.

Spencer says he told Charles that Diana, who was killed in a car crash in Paris at the age of 36, would not have wanted her boys to undergo the ordeal. He claims the prince "went ballistic" during the argument, and told him: "Rest assured, we'll forget her soon enough." Spencer also accuses Charles of having "contempt" for his ex-wife and of sounding "elated" after her death.

After excerpts of the book were published last week, Buckingham Palace responded with a strongly worded statement that's rare by the measured standards of the royal household.

"His Majesty is mindful that the pain of fraternal grief can cloud reason, affect judgment and color memory in ways others do not recognize, even many years after such a loss," it said.

Spencer has stood by his claims, insisting to the BBC that he is telling the truth. On the royal rebuttal, he asked: "Is he furious or is he embarrassed?"

War of words draws renewed attention to Charles and Diana's stormy history

Charles, then 32, married 20-year-old Lady Diana Spencer in a lavish ceremony at St. Paul's Cathedral in 1981. The couple divorced in 1996, and a decade later Charles married Camilla Parker Bowles, now Queen Camilla.

Charles Spencer, the 9th Earl Spencer, has long clashed with the royals over their treatment of his older sister.

Tensions between the palace and the Spencer family following her death were dramatized in the film "The Queen" and the Netflix series "The Crown."

In a searing eulogy at his sister's funeral, Spencer vowed that her "blood family" would carry on her "imaginative and loving" legacy in raising her two sons. The speech was widely considered a swipe at the royals.

At the time, many in Britain and beyond felt Queen Elizabeth II and her kin were too slow to acknowledge the global outpouring of grief over Diana's death and that the monarchy was deeply out of touch with the public mood.

Diana tried to break off engagement to Charles and back out of wedding

After days of news stories that pitted one Charles against another, the book landed in shops with a new offering of salacious allegations.

Spencer says his sister tried to break off her engagement after discovering Prince Charles had bought a bracelet for Camilla. She also tried to back out of the wedding, telling her father it was clear Charles didn't love her.

"My father was appalled and said it was impossible to pull out of such an enormous commitment at that point," Spencer wrote.

Diana had suicidal thoughts and more than once drove to the famous chalk cliffs at Beachy Head on the south coast of England and considered "ending it all," her brother said.

Spencer, like his nephew Prince Harry, holds the press responsible for the car crash that killed Diana, saying the paparazzi were the "leading cause of her death."

'Swan Song' is in ample supply and offered at half price

The book was prominently displayed in windows and stacked on tables in London bookshops. The 28-pound ($37.43) hardback was offered Tuesday at half price in some shops and early sales were not brisk.

Mary Scheible, a retired pharmacist visiting from Atlanta, said she couldn't wait to get back to her hotel to start reading it.

Scheible was married the same year as Diana and Charles and has always been fascinated with the princess's story.

"I wanted to see her brother's side of the story and what he had to say," Scheible said. "I'd really like to read the book in its entirety and see if what's being said is really what he's trying to convey in the book or not."

The Telegraph gave the book a two-star review (out of five) and called it a "monument" to Spencer's ego and not a book about his sister.

The Times of London said it went beyond defending Diana to launch a "Shakespearean blood feud between two aristocratic houses — a Montague-versus-Capulet drama played out in Barbour jackets and tweed where an 'ancient grudge' becomes 'new mutiny.'"

After broadcaster Piers Morgan threatened to sue over allegations of what he called "examples of brazen falsity," Spencer apologized for getting at least one of his facts wrong. But he reiterated that Morgan was surly when Spencer told him he was not welcome at his sister's funeral.

Morgan said he still planned to sue to have the "lies" removed from the book.

Charles Spencer says press treatment of Harry echoes that of his mother

The royals have spent decades putting that period of crisis behind them. The warmer, more personable approach of William and Harry — and, in recent years, the king — is a legacy of that time.

In his book, Spencer also criticized the royals for what he described as a "lack of obvious care" for the then 12-year-old Harry.

He recounted how "tiny, and slight, and bereft" his nephew looked after the funeral. "He needed Diana's hugs, of course, and they would forever be denied him," he wrote. "But instead of calm and nurture, he was allowed to spin out of control."

Some critics have questioned why Spencer felt the need to revisit the pain and trauma 30 years on.

The aristocrat said he wanted to write down his own thoughts and memories about Diana, "once and for all, rather than having the discomfort of again reading the opinions of others, many of which are based on untruths."

Asked if the relationship between the press and Harry and his wife, Meghan, mirrors the way the media treated his sister, Spencer told the BBC: "(Diana) was really brought low by all that criticism. I suppose it's a pity when I see echoes of that now."

Penguin Press said the book will be published globally and translated into 12 languages.