Prince Harry says his older brother Prince William knocked him to the floor during a 2019 argument over Harry's wife Meghan in his much-awaited memoir.
In his book Spare, Harry also discloses how the brothers, the sons of King Charles, had begged their father not to marry his second wife Camilla, now Queen Consort, and that he had taken cocaine as a teenager.
The book was due to be published on 10 January, but the Guardian newspaper printed leaked extracts overnight, and Reuters and other media have been able to obtain Spanish-language versions which went on sale early in Spain.
Details of its contents also come as ITV released a clip of an upcoming interview with Harry in which he said he could not commit to attending his father's coronation in May and defended his decision to speak out.
Harry's memoir gives a personal account of his struggles dealing with the death of his mother Princess Diana, his time in the military - when he said he killed 25 Taliban insurgents while serving in Afghanistan - and his conflicts with the press.
But the most striking revelations concern the relationship with his family, something which has hung like a shadow over the British royals since he and Meghan stepped down from official duties in 2020 to move to California to forge a new life.
As is usual for the royal family, spokespeople for King Charles and Prince William have declined to comment.
Harry wrote in his memoir that his brawl with William took place in 2019 at his then London home after his brother had called Meghan "difficult", "rude" and "abrasive".
"He grabbed me by the collar, ripping my necklace, and he knocked me to the floor," Harry wrote.
"I landed on the dog's bowl, which cracked under my back, the pieces cutting into me. I lay there for a moment, dazed, then got to my feet and told him to get out."
William then challenged his younger brother to hit back but Harry refused. William later returned to the scene, "looking regretful, and apologised", Harry wrote, with his brother asking him not to tell Meghan that he had "attacked" him.
William and Harry were once seen as very close after the death of their mother in a Paris car crash in 1997. But the brothers have fallen out since Harry married Meghan, a former actress, in 2018 and the couple then quit their royal role.
In another section of the book, Harry refers to his first meeting with Camilla, whom Diana had blamed for the break-up of her marriage. Harry says he and William had approved of Camilla but asked their father not to marry her. They later wed in 2005.
"Despite the fact that Willy and I asked him not to do it, my father went ahead," Harry wrote. "Despite the bitterness and sadness we felt in closing another loop in the history of our mother, we understood this was irrelevant."
Stinging criticism
Since their exit from royal life, the Duke and Duchess of Sussex, as Harry and Meghan are officially known, have delivered stinging criticism of the Windsors and the British monarchy which has included accusations of racism which William himself has dismissed.
Last month their six-part Netflix documentary, which attracted record audiences, aired with renewed accusations including that William had screamed at Harry during a crisis summit to discuss his future.
The main criticism from Harry and Meghan is that royal aides not only refused to hit back at hostile, inaccurate press coverage but were complicit in leaking negative stories to protect other royals, most notably William.
Prince Harry tells @andersoncooper he was the target of press leaks after private conversations with members of the Royal Family. https://t.co/0xN8FdapYV pic.twitter.com/FRKfp8AVKp
— 60 Minutes (@60Minutes) January 2, 2023
"I don't know how staying silent is ever going to make things better," Harry said in Thursday's ITV clip.
Asked why he was invading the privacy of his family, something he had railed against, he replied: "That will be the accusation from the people that don't understand or don't want to believe that my family have been briefing the press."
“The door is always open.”
— ITV (@ITV) January 5, 2023
Prince Harry sits down for an exclusive interview with Tom Bradby this Sunday at 9pm on ITV1.
Harry: The Interview | Watch on ITV1 or stream on ITVX at 9pm on Jan 8.@tombradby #ITV #ITVX pic.twitter.com/dJotkK7pOz
The title of his book Spare comes from an oft-cited quote in British aristocratic circles about the need for an heir, and a spare.
Harry says Charles reputedly said to Diana on the day he was born: "Wonderful! Now you've given me an heir and a spare, my work is done."
How much the disclosures will resonate with the public is unclear. A YouGov poll this week found 65 percent of those surveyed were "not interested at all" in his upcoming book, while another found greater sympathy among respondents for William and his wife Kate than for Harry and Meghan.
Charles himself is still hoping for a reconciliation with his son, unnamed sources told newspapers this week.
In its leaked extracts, the Guardian says the king had stood between his two sons during a difficult meeting at Windsor Castle following the April 2021 funeral for their grandfather Prince Philip, the late Queen Elizabeth's husband.
"Please, boys," Harry quoted his father as saying. "Don't make my final years a misery."
-Reuters