'Fifty Shades of Grey' may have begun life as 'Twilight' fan fiction, though British writer E.L James has certainly transcended her inspiration, having sold one million copies of the erotic sensation. The book is the fastest adult paperback novel to reach the figure, smashing the previous record set by Dan Brown's 'The Da Vinci Code'.

'Fifty Shades of Grey' shifted one million copies in just 11 weeks, though it took more than triple that amount of time for Brown to sell the same. The book also broke the weekly record for paperback sales, selling 397,889 copies and beating JK Rowling's 'The Tales of Beedle the Bard' by some 30,000 copies. It appears as though readers finishing 'Fifty Shades of Grey' are hungry for the sequels, and 'Fifty Shades Darker' sold 245,801 copies last week, while the third book 'Fifty Shades Freed' sold 212,832 copies. The books outsold the rest of the Top 50 by about two-to-one, and the first book has now become the 32nd bestselling book of all time.

Whatever Universal Pictures paid for the rights to the movie adaptation, it's probably looking more of a bargain every-day. The likes of Kristen Stewart, Robert Pattinson, RYAN GOLSING, Ian Somerhalder and Lily Collins are all thought to be in the running for the lead roles, and it's likely to be a smash-hit at the box office.