After weeks of leaked passages and pre-publication interviews, Prince Harry’s book, Spare, finally hit shelves on Tuesday—and has subsequently been flying off them. The autobiography has reportedly recorded more than 400,000 purchases in its first day, making it the fastest-selling nonfiction book in the United Kingdom. “We always knew this book would fly but it is exceeding even our most bullish expectations,” said Larry Finlay, the managing director of Transworld Penguin Random House, in an interview with The Guardian. “As far as we know, the only books to have sold more in their first day are those starring the other Harry [Potter].” The figures counted include sales for hardback copies, ebooks and audio files. “It is likely to be one of the biggest books of the year in terms of sales and impact,” said Philip Jones, the editor of book publishing magazine The Bookseller, according to the PA News Agency. Harry’s interview with 60 Minutes in the U.S. on Sunday night also delivered the show its biggest audience of the season, CBS said in a statement.