"Spare," a memoir by the UK's Prince Harry, officially went on sale on Tuesday as bookstores in London opened at midnight to meet high customer demand, local media reported.
The name of the book comes from a traditional usage among royal families as the first son is the heir and the second is a "spare" in case anything happens to the first-born.
In his book, Harry accuses his royal family, even claims a physical attack by his elder brother Prince William, as their relationship suffered over Harry's marriage to US actor Meghan Markle.
William "set down the water, called me another name, then came at me," wrote Harry. "It all happened so fast. So very fast."
The younger brother continued: "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 also said William urged him to hit back, like the fights they had as children, but he refused.
British readers have already received their copies of the autobiography days before its global release.
The famous bookshop Waterstones reportedly said Harry's book has been one of its "biggest pre-order titles for a decade."
On a US television last year, the couple complained of racism towards Markle in the Buckingham Palace.
They alleged that at least one senior family member questioned the skin color of the couple's then-unborn baby Archie and that Meghan faced huge emotional pressure in the palace.
