"Fifty Shades of Grey" trilogy dominates Amazon U.K., outsells Harry Potter series

The Writer's Coffee Shop

(CBS News) The "Fifty Shades of Grey" trilogy has dominated the Amazon U.K. e-book charts. And now it's threatening a publishing powerhouse. 

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The erotic trilogy, written by E.L. James, became a viral hit as an independently published e-book before getting picked up by Vintage Books. Now it seems like the Fifty Shades trilogy has outsold the Harry Potter series on Amazon U.K.

According to The Verge, the trilogy has sold over four million copies in print and on the Kindle since March 2012. In the past few weeks, the first book in the series, "Fifty Shades of Grey," has outsold "Harry Potter and the Deathly Hallows" two to one.

"Fifty Shades of Grey" was originally published in May 2011 by Australian publishing house, The Writers Coffee Shop. The novel was originally written as "Twilight" fan fiction with an edge. After becoming a hit, the novel was at the center of a bidding war, which was won by Vintage books - a subsidiary of Random House. A film is currently in development.