Both the X-Men movies and the Marvel Cinematic Universe are franchises that have spent years establishing deliberately sovereign continuities, and it’s going to take some creativity to figure out exactly how they can dovetail.
When all is said and done, the X-Men will become a part of the Marvel Cinematic Universe.
In the year 2000, the X-Men franchise was born, and would ultimately change the movie industry forever.
Of course, what is totally unclear at this point is exactly how that is going to happen.