Matthew Vaughn will be the director of X-Men: First Class, despite having turned down the role recently. A large part of this reversal apparently comes from support of the director of the original X-Men, Brian Singer.
While Vaughn did initially pass because of deal making issues, Singer continued to talk to him and appreciated Vaughn’s vision for X-Men, while Vaughn eventually realized what a great opportunity it was for his career, which led to a resumption of talks with Fox.
Although Fox wants to get an X-Men movie made by as soon as next summer, they also want a good film and they were impressed by Vaughn’s recent Kick-Ass. The film will open June 3, 2011 and will focus on the adventures of Professor X and Magneto when they were younger.
Source: The Hollywood Reporter