The director served as a producer on the first of these prequels, and contributed to early drafts of the screenplay, when it was known as X-Men Origins: Magneto.
Matthew Vaughn was originally suppose to return as a director on X-Men: Days of Future Past, but he dropped out for reasons unknown. He is still attached to the project, though, and is close to signing on as a producer alongside Simon Kinberg and Lauren Shuler Donner. He also contributed to the story. It is unclear at this time if Bryan Singer will contribute rewrites to the current draft of the screenplay, which has been done for some time.
James McAvoy and Michael Fassbender are set to return in the leads as Dr. Charles Xavier and Magneto, respectively.