Within days of its release, Prince Harry's controversial book has become the UK's highest selling memoir ever - with a rumour that three more could be in the pipeline.
With thousands of copies sold, it is raking in millions of pounds, and a publishing expert believes the Duke of Sussex could be tempted by the large sum of money to continue writing.
Since January 10, a staggering 750,000 copies of Spare have been sold across hardback, audio and eBook. According to official figures from Nielsen BookScan, almost 470,000 were bought in print and all of these sales in total were worth £6.6 million in the UK alone.
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Nielsen, Guinness World Records and Waterstones also confirmed it is the fastest-selling nonfiction book since UK records began in 1998. The Mirror reports.
Trailing behind four Harry Potter books by J.K. Rowling and Dan Brown's The Lost Symbol, Spare is the sixth fastest-selling book ever. Managing Editor of The Bookseller Tom Tivnan said: "It's a phenomenal number, and probably a lot more than the publisher would have dreamed of really.
"Non-fiction doesn't really sell in these numbers normally. 250,000 copies would be an amazing goal in the first week, but 470,000 is historic. It's the fastest selling non-fiction, adult hardback book of all time.
"I think the publishers are probably deliriously happy. It's an amazing number for the first week but they paid a big advance. We'll see if sales keep coming - I expect they will."
Mr Tivnan also added: "I believe Harry does have a four-book deal, but it is shrouded in secrecy. That's what's rumoured.
"I don't know if he'll do something like this again - a memoir so personal - but probably something very worthy and princely, let's say. The sales will give the publisher something to think about, and maybe they'll follow up harder for a second book."
Despite sections of the book being leaked after accidentally going on sale in Spain prior to its official publication date, Tivnan doubts this would have impacted the memoir's sales figures negatively.
He said: "Bits that had leaked and prior appearances helped to wet the public's appetite. The Netflix documentary also helped.
"If tonnes of excerpts were released prior to publication then it could've hurt sales, but I think the Sussexes' narrative was that you have to read it in context, rather than from tabloids picking and choosing, and that probably helped as well."
Mr Tivnan also acknowledged that the book was slashed to half price within the first week but argued the price cut wasn't to do with lack of demand. He said: "Any big hardback title in first few weeks of sales will be half price generally at places like WHSmith and Amazon. The average selling price is £14, but that's something to be expected.
"The second best selling book of the week is a cookery book which is half price too. The bottom line is that I think it's a really good result of the publisher.
"They were selling a big celebrity book in January, which is a massive gamble because it's normally the time for cookery and diet books in the New Year, so I think they're probably quite happy with how it's gone."
The publisher said that the English edition of Spare sold over 1,430,000 units in all formats in the US, Canada and the UK when it first appeared on the shelves of bookshops.
When announcing the record figures, Larry Finlay, Managing Director of Transworld Penguin Random House, said: "We announced last week that SPARE was the fastest selling non-fiction book ever on its first day of publication, a record that has been confirmed by Guinness World Records.
"We now know that it is also the biggest selling memoir ever in its first week of publication."
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