Deadpool director Tim Miller dropped out of the wisecracking Marvel superhero’s sequel over creative differences concerning the 2018 film.

Miller, a title sequence animator and visual effects supervisor on video games, was in the process of working on the Deadpool 2 script when the creative differences arose, with sources telling The Hollywood Reporter that star Ryan Reynolds and Miller differing on the direction of “the Merc with a Mouth.”

In April, 20th Century Fox confirmed that Reynolds, Miller and co-screenwriters Rhett Reese and Paul Wernick would all return for the sequel. As hinted in a post-credits scene, Deadpool will likely be joined by the comic book character Sable in the sequel, the filmmakers said at CinemaCon.

Miller is often credited with helping to bring Deadpool to the big screen: After the film loitered in development for years after Reynolds initially appeared as the character in 2009’s X-Men Origins: Wolverine, it was Miller’s leaked Deadpool test footage, and the viral response to the footage, that helped convince Fox to embark on the project.

Miller signed on to helm Deadpool in 2011, five years before it hits theaters. Deadpool eventually became the highest-grossing rated-R film of all time, grossing $782 million worldwide on a paltry (by superhero terms) budget of $58 million.

As Deadline notes, Deadpool is an especially important Marvel franchise property to Fox now that Hugh Jackman is closing the book on Wolverine following the upcoming Logan in March 2017.

Miller’s split with the sequel and Fox studio is said to be amicable, as the director will immediately jump onto another Fox property, Influx, the first installment of a planned trilogy.

‘Deadpool 2’ Loses Director Over Creative Differences