Prince William and Kate encouraged Prince Harry to wear a Nazi costume to a fancy dress party, it is reported.
The Duke of Sussex, aged 20 at the time, caused outrage when he was pictured wearing the soldier's uniform complete with a swastika in 2005.
He recently addressed the incident during the third episode of Harry & Meghan, the Netflix docuseries, saying it was "one of the biggest mistakes of his life".
Now, in a leaked extract from his new memoir Spare, Harry has shifted some of the blame for the scandal to his brother and sister-in-law.
He writes about asking for William and Kate 's advice on choosing between two outfits - a pilot's costume or the Nazi uniform.
In a segment of the book, obtained by Page Six, Harry writes: "I phoned Willy and Kate, asked what they thought. Nazi uniform, they said."
He goes on to say that when he went home and tried it on for them, they "both howled".
"Worse than Willy's leotard outfit!", he adds. "Way more ridiculous! Which, again, was the point."
His comments come as a separate leaked extract from the book, to The Guardian, alleges that he was physically attacked by Prince William in a row over his marriage to Meghan Markle.
Harry alleged the confrontation took place at his London home in 2019 and had left him with a visible injury to his back after the Prince of Wales grabbed his brother by the collar and ripped his necklace before knocking him to the floor.
Harry further claimed William had called the American actress "difficult", "rude" and "abrasive" - comments which the younger brother said parroted "the press narrative" about his wife.
Kensington Palace has declined to comment on the allegation.
According to the newspaper, the "extraordinary scene" is "one of many" in Spare which is due to be published on January 10.
The article goes on to say that, according to Harry, his elder brother had wanted to discuss "the whole rolling catastrophe" of their relationship and struggles with the press.
But when William arrived at Nottingham Cottage - where Harry was then living - in the grounds of Kensington Palace, the Prince of Wales was already "piping hot".
"After William complained about Meghan, Harry writes, Harry told him he was repeating the press narrative and that he expected better," The Guardian reports.
"But William, Harry says, was not being rational, leading to the two men shouting over each other.
"Harry then accused his brother of acting like an heir, unable to understand why his younger brother was not content to be a spare."
Insults were then exchanged between the two men, before William claimed he was trying to help, claims which Harry found incredulous, and informed his brother of such, angering William.
So much so, Harry writes, the Prince of Wales swore and stepped forwards, scaring him.
He writes: "(William) called me another name, then came at me. It all happened so fast. So very fast.
"He grabbed me by the collar, ripping my necklace, and he knocked me to the floor. 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."
Harry writes that William urged him to hit back but he refused. Shortly afterwards though, the elder brother apologised.
William had then told his brother not to tell Meghan about the confrontation, resulting in Harry saying: "You mean that you attacked me?", to which William responded: "I didn't attack you, Harold."
Harry said he did not immediately tell his wife but she had noticed "scrapes and bruises" on his back.
Earlier in the memoir, the duke reportedly elaborates on the story behind the book's title, Spare. According to The Guardian, he recounts what the King said to Diana, Princess of Wales on the day of his birth.
His father, Harry claims, told the then-Princess of Wales: "Wonderful! Now you've given me an heir and a spare - my work is done."
The duke's extraordinary book claims come after the release of a teaser trailer from an ITV interview in which Harry said he wants his father and brother back.
The interview, due to be released on Sunday, will be broadcast two days before Spare is published around the world.
