EXCLUSIVE: Matthew Vaughn has decided not to direct the sequel to 20th Century Fox‘s hit spinoff X-Men: First Class. Ready for the next shocker? Atop the studio’s replacement short list is Bryan Singer, who launched the X-Men feature franchise with the first two superb films and who has been a guiding influence in this spinoff by writing the treatment and producing. If this works out, Singer and Vaughn would essentially be switching roles. Vaughn, who wrote the treatment for the sequel for X-Men: Days Of Future Past that was scripted by Simon Kinberg, would step back to produce the film with Kinberg and Lauren Shuler Donner.

Vaughn will do another film for Fox, and I’m hearing it will be the drama Secret Service, an adaptation of the Mark Millar comic book series that Vaughn has been working on with the author.

Fox already has the script for X-Men: Days Of Future Past, and set to return is Fox’s First Class cast that includes Michael Fassbender, James McAvoy and Jennifer Lawrence. Fox hopes to make the July 18, 2014 release date it set for the sequel, but it will have to find a director quickly. I’m not exactly sure why Vaughn is bowing out, but he is pretty picky on projects that he directs. You’ll recall that he briefly bowed out of the original First Class film, prompting Fox to start a search before he changed his mind and returned. Vaughn also passed on directing the sequel to his Kick-Ass film, entrusting the job to Jeff Wadlow. Wadlow is shooting Kick-Ass 2: Balls To The Wall right now with Aaron Johnson and Chloe Moretz.

The studio just navigated a similar situation when Rupert Wyatt decided not to come back and direct the sequel to Rise Of The Planet Of The Apes. The studio had a cream of the crop group of directors waiting to take Wyatt’s place, and the search ended when Fox’s top choice, Cloverfield helmer Matt Reeves, committed to the job.

Fox has been trying to up the pedigree of directors who make films at the studio, and bringing back Singer while keeping Vaughn in the fold would be a pretty good feat. The studio did not immediately comment, but I’ll update my story when I have more information. Singer’s next film is Jack The Giant Killer for New Line.