So a lot of people are saying that X-men: First Class doesn't fit continuity-wise with the third film. For those of you who (are smart!) have forgotten, the opening of The Last Stand has Professor X and Magneto in the 80's talking to a young Jean Grey. However, the First Class ends with Xavier and Magneto becoming enemies.
So does First Class erase The Last Stand?
Considering the complicated nature of the relationship between the two characters, it’s not that much of a stretch to believe that at some point during the twenty years between the two films, Xavier and Magneto tried to reconcile their friendship. Also, since what they did the same thing with young Jean that they did together in First Class with the other young mutants, I’d say that not only is First Class is very much in continuity with The Last Stand.
Then again, I totally approve of the idea that The Last Stand never happened.