E.L. James's Fifty Shades trilogy can now proudly boast a new nickname: 100 Million Shades of Grey. This week, the erotic book series reached a milestone.

On Wednesday, Vintage Books announced that the trilogy, consisting of Fifty Shades of Grey, Fifty Shades Darker and Fifty Shades Freed, sold 100 million copies around the world. Almost half of those sales, 45 million to be exact, were courtesy of United States readers, Los Angeles Times reports.

"The Fifty Shades trilogy struck a chord around the world that continues to resonate," Anne Messitte, publisher of Vintage/Anchor Books in the U.S., said in a statement. "We see new readers coming to the books every day, and the sales, two years after our initial publication, remain strong and steady."

James originally self-published Fifty Shades of Grey, which began as fan fiction inspired by Stephenie Meyer's Twilight series. Vintage Books, a part of the American publishing company Random House, bought the book in March of 2012. Within weeks, all three books were available. The series became one of publishing history's best-selling series, New York Times reports.

Vintage Books' news means that James's books have joined the likes of Carolyn Keene's Nancy Drew stories, Ian Fleming's James Bond books, J.K. Rowling's Harry Potter series and Meyer's Twilight tales.

In addition to reaching the 100 million milestone, as of Sunday, the Fifty Shades trilogy has enjoyed 100 weeks on the highly coveted New York TImes best-seller list.

Interestingly enough, the popularity of the three erotic novels does not represent a trend in erotic literature. According to booksellers, other erotic books have not seen an increase of sales since the release of the Fifty Shades trilogy.

A Fifty Shades of Grey movie starring Jamie Dornan and Dakota Johnson as Christian Grey and Anastasia Steele respectively hits theaters Feb. 13, 2015.

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