According to its publisher, Prince Harry's memoir "Spare" has experienced the fastest non-fiction book sales in the U.K. ever.

According to Transworld Penguin Random House, which cited British sales data, 400,000 copies of the book have already been sold in hardcover, e-book, and audio versions since its formal release on Tuesday.

"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)”

Now that’s a remarkable feat!