Prince Harry reportedly claims in his highly anticipated memoir that Prince William and Princess Kate told him to wear a Nazi uniform and "howled" when they saw it.

In 2005, Prince Harry was photographed wearing a Nazi costume at a “Native and Colonial” theme party, sparking widespread outrage at the time, and in a recent Netflix documentary, Harry called it “one of the biggest mistakes” of his life.

But in fresh revelations, first reported by US gossip site Page Six, the estranged son of King Charles writes in his upcoming book that he phoned William and Kate to ask their opinion on whether he should wear a pilot uniform or a Nazi costume to the party, and they chose the latter.

In the segment obtained by the US publication, Harry writes: “I phoned Willy and Kate, asked what they thought. Nazi uniform, they said."

He adds that when he went home and tried it on for them, “They both howled. Worse than Willy’s leotard outfit! Way more ridiculous! Which, again, was the point.”

Untitled design (37)

Prince William, Princess Kate, and Prince Harry in 2016 (L) and The Sun front page with a photograph of Harry wearing the Nazi outfit (Photos via Getty Images)

In an episode of the Duke and Duchess of Sussex's Netflix documentary released last month, Harry cut a contrite figure as he reflected on the outrage he sparked when he wore the uniform, complete with a swastika.

Harry said: “It was probably one of the biggest mistakes of my life. I felt so ashamed afterwards. All I wanted to do was make it right.”

He added: “I could’ve just ignored it and probably made the same mistakes over and over again in my life. But I learned from that.”

Harry, who was aged 20 at the time, was pictured holding a drink and cigarette while wearing the costume.

At the time, Clarence House issued a response saying Harry had apologised for any offence or embarrassment caused.

This is not the first time Prince William has been accused of helping choose the outfit. In his 2020 book “Battle of Brothers", Royal Historian Robert Lacey wrote: “Harry chose his costume in conjunction with his elder brother — the future King William V, then 22, who had laughed all the way back to Highgrove (Charles’ country home) with the younger sibling he was supposed to be mentoring — and then onwards to the party together.”

According to Lacey, the fact that Harry was forced to bear the brunt of the public outrage caused him to feel alienated from his family.

A former aide told him: “For the first time, their relationship really suffered and they barely spoke. Harry resented the fact that William got away so lightly.”

Harry's upcoming memoir, entitled 'Spare', is expected to go into detail about the falling out with his older brother, William, and his father, King Charles II.

In another extract from the book published today by The Guardian, Harry describes a physical confrontation between the brothers at his London home in 2019 that he says resulted in a physical injury to his back.

Harry claims that William called Meghan “difficult”, “rude” and “abrasive”, which Harry describes in the book as a “parrot[ing of] the press narrative” about his American wife.

The disputed then escalated, and according to Harry, William “grabbed me by the collar, ripping my necklace, and … knocked me to the floor”.

The latest controversial revelations are reportedly one of many in Harry's memoir, 'Spare', which is due to be published worldwide next week.

Representatives for Prince William and Princess Kate have been approached for comment.

READ MORE: Nazi costume was one of the biggest mistakes of my life, says Prince Harry