Joss Whedon has left the Batgirl feature film project, which he had been tapped to both write and direct, according to The Hollywood Reporter. Whedon came into the project in March 2017; sources say that after nearly a full year, he struggled to figure out what Batgirl as a film should be.

“Batgirl is such an exciting project, and Warners/DC such collaborative and supportive partners, that it took me months to realize I really didn’t have a story,” Whedon told The Hollywood Reporter in a statement. He also thanked DC President Geoff Johns and Warner Bros. Picture Group President Toby Emmerich for being understanding when he needed to step back.

Whedon is best-known as the creator of Buffy the Vampire Slayer as well as the director of 2012’s The Avengers and 2015’s Avengers: Age of Ultron. He also took over Warner Bros.’ production of Justice League when director Zack Snyder left the production of that film.

It is currently unknown who, if anyone, will be replacing Whedon on the Batgirl film.