Prince Harry Calls Prince William His 'Beloved Brother' and 'Archnemesis' in Book

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Prince Harry is "not holding anything back," says Good Morning America host Michael Strahan after the Duke of Sussex sat down for an interview with him.

In a preview of their sit down, which will air in full on Monday morning ahead of the release of Harry's memoir Spare the following day, Strahan says that Prince Harry referred to his brother Prince William as both his "beloved brother" and his "archnemesis" in the book.

"Strong words. What did you mean by that?" Strahan asked.

Prince Harry, 38, replies, "There has always been this competition between us, weirdly."

"I think it really plays into, or was played by, the 'heir/spare,' " he continued, referring to Prince William's role as the future king while he has moved down the line of succession as Prince William and Kate Middleton had children.

RELATED: Everything to Know About Prince Harry's Upcoming Memoir: 'I'm Writing This Not as the Prince'

Speaking with his cohosts, Strahan said that he had read Prince Harry's book, which includes insight about the grief over the death of his mother Princess Diana when he was 12, his time in the military and his role as a husband to Meghan Markle and father to son Archie Harrison, 3, and daughter Lilibet Diana, 1.

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"He is not holding anything back," Strahan said. "I read the book from the front page to the last, and you're amazed at how open he is."

In a leaked extract of the memoir published by The Guardian on Wednesday, Prince Harry claimed that Prince William physically attacked him during a confrontation about Meghan in 2019 at Nottingham Cottage, where the Duke and Duchess of Sussex lived on Kensington Palace grounds after their wedding.

Daniel Leavl-Olivas-Pool Getty Images Prince William and Prince Harry

William reportedly called Meghan "difficult," "rude" and "abrasive," to which Harry replied that his brother was simply "parrot[ing of] the press narrative" about his wife. The Guardian reports that Harry then accused his brother of acting like an heir, after which insults were exchanged. William reportedly claimed he was just trying to help.

The argument turned physical, with Harry reportedly writing that William "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 says he called his therapist, but it was only when Meghan noticed "scrapes and bruises" on his back that he says he revealed the incident to his wife.

Chris Jackson/Getty Images Prince William and Prince Harry

It was previously announced that Prince Harry sat down for two other interviews that will air on Jan. 8, two days before the memoir's release. Both the British outlet ITV and CBS News' 60 Minutes shared portions of their interviews with the Duke of Sussex.

"It never needed to be this way," Harry told ITV's Tom Bradby in a preview. He went on to refer to "the leaking and the planting" of stories in the British press before telling Bradby, "I want a family, not an institution."

PENGUIN RANDOM HOUSE The book jacket of Prince Harry's memoir 'Spare'

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In an interview with Anderson Cooper for 60 Minutes, Harry expanded on allegations of "leakings" in the media and how negative stories have affected him and Meghan. He also told Cooper why he's addressing these matters publicly.

"Every single time I tried to do it privately, there have been briefings and leakings and planting of stories against me and my wife," Prince Harry said. "You know, the family motto is 'never complain, never explain' … it's just a motto and it doesn't really … hold."