A paperback edition is expected in the coming months, with a planned first run of some 500,000 copies.
Despite the popularity of the titles — both are fixtures on the Amazon bestseller list in their category — next to nothing is known about the author, Sylvain Reynard.
The person behind the nom de plume is believed to be a man by some and a woman by others. Interviews with Reynard — who went by Sebastien Robichaud when the Gabriel novels were still available on fanfic sites — suggest he or she is Canadian and has already published several non-fiction books.
Previously known as "The University of Edward Masen," Gabriel's Inferno and Gabriel's Rapture revolve around the misadventures of Professor Gabriel Emerson, a handsome and sophisticated Dante scholar with a dark past who uses his wiles to seduce a "sweet and innocent" grad student.
The announcement of the Gabriel deal comes at a momentous point in time for the so-called "mommy porn" genre: Fifty Shades Of Grey, which itself began life as Twilight fanfic, has just surpassed the last book in JK Rowling's Harry Potter series to become Amazon UK's bestselling book of all time.