Foreign rights to Audrey Carlan's bestselling Calendar Girl, the 12-book erotica series that broke out earlier this year, have now been sold in 27 countries. Bookcase Literary Agency's president and partner Flavia Viotti, who brokered the deal in conjunction with series publisher Waterhouse Press, confirmed that, in some countries, the series has fetched advances up to seven figures.

Calendar Girl, which started as an indie series self-published by Carlan, was picked up by Waterhouse Press in 2015. The books follow a young woman who becomes a high-end escort in order to pay off her family debts--each title is named for a different month of the year--and began breaking out on several e-book bestseller lists in early 2016. In January, USA Today touted the series as "the next Fifty Shades of Grey."

According to Waterhouse, the series has sold more than 2.5 million copies in the U.S. to date and is already a bestseller in Denmark—the only territory outside of the States where the series is currently published.

Speaking to the international sales success of the series, Viotti said international editors quickly responded to Carlan's book. "One week after the series hit #1 on the New York Times bestseller list, I was running auctions in six different countries at the same time," she said.

Among the 27 publishers which have acquired the series are Spain's Editora Planeta, France's Hugo, Italy's Mondadori, and Germany's Ullstein.