deadpool 3: Deadpool 3 Director acknowledges X-Men's role in MCU sequel, here' what he said
The cinematic history of the X-Men has been marked by rights disputes. In the 1990s, Marvel had to sell the film rights to the X-Men to Fox to avoid financial troubles. Fox achieved significant success with the X-Men franchise, particularly with Ryan Reynolds' Deadpool films, which became some of the highest-grossing R-rated movies ever.
Source: indiatimes.com