It is widely known that Fifty Shades of Grey originally started out as Twilight fan fiction, but soon progressed to a full-blown phenomenon. It's been dominating bestseller lists since it was released, creating havoc in the book-reading community, and is now being turned into a movie by one of the best producing teams in Hollywood.
At an autograph signing, a rep for the publishing company behind Fifty Shades reportedly announced that there would be a fourth 'Fifty Shades' book. One of the members in the line is said to have asked a couple of questions to the rep, and the rep's answers were that there was definitely a fourth one, and that the author apparently just 'threw it' to her publisher. The rep also reportedly saw the first give pages of the book, and he says it definitely exists.
In all honesty, it would make absolute sense for James to write a fourth Fifty Shades book. Fans have been clamoring for more since the end of the third novel, and I'm sure James would appreciate another paycheck as these books have made her a millionaire. Who would say not to adding another couple of million to the coiffer?