Prince Harry claims he knew immediately he and brother William would have a heated row when he arrived at his door before he broke his necklace and knocked him to the floor.
In his new book, Spare, the Duke of Sussex recounts the alleged physical attack at his London home in 2019 after the future king called wife Meghan Markle "difficult" and "abrasive".
Harry felt his older sibling was simply parroting "the press narrative" before the confrontation escalated.
He said he was left with a visible back injury during the scuffle.
The bombshell memoir is set to be released next week and is likely to prove difficult reading for the Royal Family.
The Duke - who stepped down from the Firm in 2020 and now lives in the US - said that William had wanted to talk about "the whole rolling catastrophe" of their relationship and press issues.
But when the next-in-line arrived at Nottingham Cottage, in the grounds of Kensington Palace, he was already "piping hot".
The two royals are then said to have begun shouting over each other and insults were exchanged.
The Guardian reports, Harry then claims he said: “Are you serious? Help me? Sorry – is that what you call this? Helping me?”
He said William swore while stepping towards him as he walked into the kitchen.
Harry describes giving his brother some water and telling him: “Willy, I can’t speak to you when you’re like this.”
The now-Prince of Wales is said to have put down the water and closed in on his brother.
Harry writes: "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.”
William then allegedly tried to goad his brother into a fight as they had as children, but Harry refused before William apologised.
But as he left, Harry said William told him not to tell Meghan.
He said that he did initially keep his word but later Meghan noticed "scrapes and bruises" and became "sad" but not surprised when he revealed what had happened.
