The Forbes magazine 2013 list of top-earning authors just came out, and 50-year old "Fifty Shades of Grey" author E.L. James topped the list as the No. 1 highest paid author, US Weekly reports. Just how much money did her erotic and highly controversial book series rake in for her?

With an estimated $95 million in earnings so far, E.L. James seems to prove the theory that "sex sells." Her novels began as fan fiction for the popular "Twilight" series by Stephanie Meyer, originally entitled "Master of the Universe," and later James changed the details, including the title of the story and names of her characters, which have now become iconic and oft-referenced in popular culture.

Like the "Twilight" saga, James's three-part series will be adapted into a film, and casting is already underway. Fans are eagerly debating who will play the roles of Anastasia Steele and Christian Grey in the movie version, and currently Ian Somerhalder and Alexis Bledel are popular picks.

For most authors, you'd have to crank out novel after novel for years to make that kind of cash, Forbes magazine explains, but some get lucky by cashing in on a successful market or trend, just as Suzanne Collins did with her futuristic fantasy trilogy, "The Hunger Games," which went on to become a hit film series and spilled over into the adult marketplace. Collins's earnings of $55 million put her at No. 3 on the Forbes list, right behind James Patterson ($91 million), whose bibliography of 118 novels have sold over 270 million copies worldwide.

"When it comes to predicting a single solitary book, there's little science behind it," publishing analyst Michael Norris of Simba Information told Forbes magazine of what it takes to be successful in the publishing industry. "You can have as much access to this data as you want but there's nothing to quantify luck." 

To get the estimated earnings for each author, Forbes used a combination of sales data, published figures and industry information from between June 2012 and June 2013.

Although her "Fifty Shades of Grey" novels are complete, James is reportedly at work on her next novels, though she has remained quiet on whether or not they'll touch on the same sexual themes of "Fifty Shades."