Prince Harry’s memoir “Spare” has become the fastest selling non-fiction book ever in the U.K., according to its publisher.

After the book’s official release Tuesday, 400,000 copies have been sold so far across hardback, e-book and audio formats, Transworld Penguin Random House said, citing British sales figures.

“We always knew this book would fly but it is exceeding even our most bullish expectations,” the publishing house’s Managing Director Larry Finlay said in a statement.

“As far as we know, the only books to have sold more in their first day are those starring the other Harry (Potter),” Finlay added.

The biography includes details about the prince’s personal struggles, such as losing his mother, Princess Diana, aged 12, as well as frictions with fellow royals, including his father, King Charles III, stepmother Camilla and older brother Prince William.

“Spare” is available in 16 languages, and ranks as the best-seller on Amazon websites across the world, including in the U.K., U.S., Germany, France, Italy, Spain, Australia and Saudi Arabia at the time of writing.

Copies of the intimate memoir were mistakenly released in Spain five days before the official publication, prompting much of its contents to make headlines across the world.

Harry also gave several interviews ahead of the book launch, doubling down on claims that some royals leaked damaging stories to the tabloid press about him and his wife Meghan in order to protect their own reputations.

The royal family has not commented on the book or any of the interviews given by Prince Harry.

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