User blog comment:Jacknapier10/Which characters cannot appear in the Marvel Cinematic Universe?/@comment-25866432-20140510164147/@comment-24901406-20140511165230

Deadpool isn't in the X-Men franchise. He is separate after being sold to New Line Cinemas in 1999, but then being acquired by Fox in a rather complicated rights deal. To all intents and purposes he is legally separate, but can be used by Fox alongside their other two franchises as they please (and as long as they make a film with him every seven years).