Prince Harry reportedly claims he was physically attacked by his brother William during a row over his marriage to Meghan Markle.

The Guardian has obtained a copy of Spare – the Duke of Sussex's highly anticipated book – days before it was due to hit the shelves.

In a leaked extract, it is alleged that the Prince of Wales grabbed his brother and ripped his necklace before knocking him to the floor.

Harry goes on to claim that William had called the American actress "difficult", "rude" and "abrasive".

"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," Harry reportedly wrote in the book.

"I lay there for a moment, dazed, then got to my feet and told him to get out," the excerpt continued.

The incident allegedly took place at Nottingham Cottage back in 2019 when Harry was living there and started when William arrived and complained about Meghan.

Nazi uniform claim

According to US website Page Six, in Prince Harry's book there is also a claim that William and Kate helped him decide on his infamous Nazi uniform, which he wore to a party in 2005.

He has since described it as "one of the biggest mistakes in my life".

Sky News has approached Buckingham Palace and Kensington Palace and both will not be commenting on the allegations.

Sky News' royal correspondent Rhiannon Mills said that these are "very serious allegations".

She said: "We know in 2019 that the relationship between the two brothers was falling apart, so it wasn't unexpected to hear that they were not getting along then. But it is shocking to be given this much personal detail.

"In the past there have been criticisms of Harry that he has made damning allegations of racism within the palace or allegations that they have not taken Meghan's mental health seriously enough and some suggestions that they haven't gone far enough in naming specifics.

"It seems that Harry, in this book, is not holding back."

'You don't need to tell Meg about this'

Harry writes that his brother was not being rational and they both started shouting at each other, exchanging insults, before William claimed he was trying to help.

"Are you serious? Help me? Sorry - is that what you call this? Helping me?," Harry said, according to The Guardian's copy.

His comment supposedly angered William, and the alleged altercation took place after he offered him a glass of water.

Harry added that William urged him to hit back, before leaving and then returning "looking regretful and apologised".

When he left again, Harry said he "turned and called back: 'You don't need to tell Meg about this.'"

Harry told his therapist about the incident first

He goes on to explain that he didn't immediately tell his wife, but did tell her of the incident after she noticed "scrapes and bruises" on his back.

However, he claimed to have told his therapist first.

The book - which is entitled after the phrase "heir and a spare" - also delves into Harry's childhood, his school, his career as a royal and the relationship he shares with his parents and brother.

He recounts memories of his mother Princess Diana, who was killed in a car crash in 1997, and the Queen, who died last year.

Spare, which is due to be released on 10 January, comes after the prince's recent Netflix documentary into his life with Meghan and their decision to leave the Royal Family.

In the series, it was revealed Meghan suffered a miscarriage, which Harry said was caused by the stress put on her as a result of their lawsuit against the Daily Mail's parent company, and had suicidal thoughts.

He also claimed that William broke a promise to him never to leak stories or brief against one another after witnessing the fallout of such actions in their father's office.

Harry calls William 'beloved brother and arch-nemesis'

It has also been revealed Harry calls William his "arch-nemesis" in the memoir.

In a preview clip of an interview with Good Morning America which is set to be broadcast on Monday, presenter Michael Stahan, who said he has read the full 557 pages of Spare, asks Harry about the rift between the brothers.

"There is a quote in this book where you refer to your brother as your 'beloved brother and arch-nemesis'. Strong words. What do you mean by that?"

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

"I think it really plays into or was played by, the 'heir/spare'."

Harry refuses to commit to attending his father's coronation

The duke's extraordinary book claims also come during the release of a second teaser clip of his upcoming ITV interview, in which he refuses to confirm whether he will attend his father's coronation in May, saying the "door is always open" to his family for reconciliation - but "the ball is in their court".

Asked if he believes in the monarchy, the prince says, "yes", but when further pressed if he will play a part in its future, he replies: "I don't know."

Harry also says why he has chosen to speak out: "I don't know how staying silent will make things better."

Put to him that some people would say he has railed against invasions of his privacy all his life - and now he is invading the privacy of his nearest and dearest without permission - Harry replies: "That would be the accusation... from the people that don't understand, or don't want to believe, that my family have been briefing the press."

'I want a family - not an institution'

In an earlier teaser trailer from the interview, Harry said he wanted 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.

In a series of clips from his ITV conversation, Harry tells presenter Tom Bradby: "It never needed to be this way", and refers to "the leaking and the planting" before adding: "I want a family, not an institution."