An alarm is ringing somewhere deep within the 20th Century Fox lot today. It’s howling because Matthew Vaughn has opted to drop out of directing X-Men: First Class sequel Days Of Future Past.

Deadline was unable to dig up a specific reason for Vaughn deciding not to return for the sequel (despite already having begun work developing it). Now the studio will need to find someone else to call the shots, just as it did with Dawn Of The Planet Of The Apes when Rupert Wyatt decided to hit the ejector button built into his director's chair.

But it may not need to look that far, because word has it that Future Past’s producer, Bryan Singer, who has been guiding the retro version of the franchise so far, might just switch jobs with Vaughn and pick up the megaphone. But then again, he also has promotional duties coming up on Jack The Giant Slayer.

Whatever happens will likely happen quickly, as Fox has the script (primarily written by Simon Kinberg) in hand. Plus it has commitments from Michael Fassbender, James McAvoy and Jennifer Lawrence to return. Not forgetting the ticking clock of an announced release date: July 18, 2014.

And don’t think this points to a sudden bubbling of bad blood between Vaughn and Fox: he is still looking at making the adaptation of Mark Millar’s Secret Service for the studio.