In his new autobiography, Spare, Prince Harry says he was physically attacked by his brother William, now Prince of Wales, after their relationship was strained over his marriage to American actor Meghan Markle.

Harry wrote that William “grabbed me by the collar, ripping my necklace, and … knocked me to the floor”, according to a report by The Guardian.

This, he claimed, occurred during a confrontation in his London home in 2019 where William had called Meghan “difficult”, “rude” and “abrasive”.

The attack, Harry said, resulted in visible injury to his back.

The Guardian said it obtained a copy of Spare, which will be published worldwide next week, “amid stringent pre-launch security”.

The publication, and claims made by Harry about the altercation, is expected to spark a serious furore for the British Royal family.

The title of the book comes from an old saying in royal and aristocratic circles that a first son is an heir to titles, power and fortune, and a second is therefore a “spare”.

Harry wrote that William wanted to talk about “the whole rolling catastrophe” of their relationship and struggles with the press.

William was “piping hot”, he said, when he arrived at Nottingham Cottage on the grounds of Kensington Palace, where Harry was living at the time.

William complained about Meghan, Harry writes, but Harry told him he was just repeating press narrative and he expected better.

• Prince Harry to release an "eyebrow raising" memoir
• ‘I want my father, brother back’: Prince Harry's 'explosive' swing at royals ahead of memoir release

Harry said William was not being rational at the time and the two princes shouted over each other.

He accused William of acting like an heir and failing to understand why he was not content to be a spare.

After insults were exchanged, William claimed he was trying to help.

“Are you serious? Help me? Sorry – is that what you call this? Helping me?” Harry said.

This comment angered his brother, Harry said. Now scared, Harry went to the kitchen with William following.

“Willy I can’t speak to you when you’re like this,” Harry said as he gave Willaim a glass of water.

“He set down the water, 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 wrote that Willaim urged him to hit back, citing fights they had as kids but Harry refused to.

William then left, Harry said, then returned “looking regretful, and apologised”.

After that, Harry wrote that as William left a second time, he “turned and called back: ‘You don’t need to tell Meg about this.’

“‘You mean that you attacked me?’

“‘I didn’t attack you, Harold.’”

Harry claimed he called his therapist but didn’t immediately tell his wife.

He told her of the attack only after she noticed scrapes and bruises on his back.

Meghan “wasn’t that surprised, and wasn’t all that angry ... she was terribly sad”, Harry said.

Harry recounts a story early on about how his father, now King Charles, had supposedly told his mother, Princess Diana on the day of his birth: “Wonderful! Now you’ve given me an heir and a spare – my work is done.”

His resentment about being the “spare” is the unifying theme of his book, The Guardian said.

“Through chapters on his childhood, his schooling, his career as a royal and in the British army, his relationship with his parents and brother, and his life with Meghan through courtship, wedding, and marriage to their own experience of parenthood.”

In the book, Harry was also unsparing in his recounting of intensely private scenes and conversations with his mother Diana, who was killed in a car crash in Paris in August 1997, and his grandmother, Queen Elizabeth II.

Harry also recounted an anguished meeting with Charles and William after the funeral of Prince Phillip, the queen’s husband, at Windsor Castle in April 2021.

Charles, he said, stood between his warring sons, “looking up at our flushed faces”.

“Please, boys,” Harry quoted his father as saying. “Don’t make my final years a misery.”

Harry met Meghan in 2015 and married at Windsor Castle two years later, becoming the Duke and Duchess of Sussex.

The couple began life as working royals but soon drifted apart from the family before moving to Canada and then California after an acrimonious split.

Their famous interview with Oprah Winfrey in 2021 caused huge controversy, and subjects of that interview and a recently released Netflix documentary - including Meghan’s thoughts of suicide, her miscarriage and suggestions of racism within royal circles are extensively covered in Harry’s book.