A first edition Harry Potter book fetched $18,000 at auction Tuesday.

The winning bid for the first novel by J.K. Rowling that launched Pottermania went to an anonymous buyer. Bonhams auctioneers had estimated the book would sell for between $10,000 and $20,000.

First editions of "Harry Potter and the Philosopher's Stone" -- published in the United States as "Harry Potter and the Sorcerer's Stone" -- are valuable because of their rarity, the auction house said. The publishers produced between 500 and 1,000 copies in the book's first run.

That a book that is relatively new would fetch such large amounts is unprecedented, said Luke Battenham, Bonham's book specialist.

"The author is still alive, it's a fairly new series ... but by the time there was a third book, you could already see it would be a hit," Battenham said. "It's a phenomenon."

The sale comes less than a month before the July 21 release of the seventh and final book in the Harry Potter series. The books have sold more than 325 million copies worldwide.