A signed copy of J.K. Rowling’s first edition of “Harry Potter and the Philosopher’s Stone” was auctioned off on Thursday to an anonymous private bidder for a whooping $40,326 at Christie’s auction house in London.

The book, belonging to a young man in his twenties, is part of the small lot printed in the first run in 1997. Many of those books were instantly bought up by libraries, making unspoiled copies extremely rare.

According to Crispin Jackson, the head of books at the South Kensington branch of Christie’s, this particular book was perhaps the best of its kind.

“From Goblet of Fire onwards, the series took off so quickly that first editions were common because the print runs were huge,” he said. “The collecting buzz started with Prisoner of Azkhaban in 1999 and while the market slightly dipped before the publication of Deathly Hallows, it has picked up again with the conclusion of the series and the huge success of the films.”

“It was printed to be sold to libraries in the hope that kids would take it out and it would then become popular through word of mouth,” he said.

Other Potter-related things on sale included a publisher's proof copy of the same book in plain covers and a two signed editions, one hardback and one paperback.

At a London auction in May, a copy of “Philosopher's Stone” inscribed with a personal dedication to the owner sold for more than $55,000, including buyer's premium.

“It shows what a global phenomenon Harry Potter is,” Jackson said. “We auctioned a 250-year-old first edition of the classic Tom Jones by Henry Fielding in the same sale, but the Harry Potter went for more than ten times what we got for that.

“Some people find it hard to get their heads around that, but Tom Jones, despite being a classic, has simply never had the response Harry Potter has.”