Jamie Dornan and Dakota Johnson haven't signed on to star in the 'Fifty Shades of Grey' spin-off.

Author EL James, who penned the best-selling trilogy, announced earlier this week that she is working on a new book, 'Grey,' from the perspective of billionaire S&M enthusiast Christian Grey and has reportedly already sold the rights to Universal.

But a source told The Hollywood Reporter that the 33-year-old actor, who plays Christian, and the 25-year-old actress, who plays submissive heroine Anastasia Steele, are currently only contracted to appear in three films based on the trilogy, so there are no guarantees they will star in a future adaptation of the upcoming novel.

The insider also claims that neither of the stars had any idea that another book, which would likely serve as the fourth film in the franchise, was even being written.

While Universal declined to comment on plans for the project, the source claims the 'Grey' movie will more than likely go ahead since the first film generated $570 million at the box office worldwide.

The second film, 'Fifty Shades Darker,' has yet to begin filming, but is already scheduled to be released on February 10, 2017, while the third film, 'Fifty Shades Freed,' is set to be released on February 9, 2018.

Northern Irish heartthrob Jamie was previously forced to deny rumours he was planning to quit the risky films.

He said: ''The idea was that we honour the trilogy and do all three [movies].''

Asked whether his wife, Amelia Warner, was keen for him to quit the role because of the explicit sex scenes, he replied: ''Total b*****ks!''