Among the revelations was the story of a physical fight between him and his brother over a conversation about Meghan.
He claimed the Prince of Wales "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."
The book also claims Harry and William "begged" King Charles not to marry Camilla.
The autobiography reveals that the royal brothers were aware of Camilla as the "other woman".
Harry also revealed he killed 25 people during his tours of Afghanistan when he was in the military, saying it was something he was neither proud nor ashamed of.
Did Harry write it?
No, although the book is written in the first person it was ghostwritten by J.R. Moehringer.
The book covers his entire life from childhood, education, his time in the army and as a working royal.
Prince Harry has said the central theme of the book is his resentment at being seen as the "spare" heir to the throne behind his older brother.
The book is being published by Penguin Random House.
Spare will be released in the UK on 10 January.
Who is J.R Moehringer?
John Joseph Moeringer is an American novelist and journalist.
Be began his career working at some of America's biggest newspapers and won a Pulitzer prize for feature writing while working at the L.A Times.
He has significant experience as a ghostwriter and wrote the autobiography of tennis star Andre Agassi and Nike co-founder Phil Knight.
He has also published several pieces of non-fiction, including Sutton, based on the life of bank robber Willie Sutton.
Many of the people he has worked with have had difficult relationships with their fathers.
He also published his own memoir, The Tender Bar, of his life in 2005 focusing on the first three decades of his life, where he discussed his difficult family life.
The book was turned into a film in 2022 directed by George Clooney and starred Ben Affleck.