The X-Men have dealt with basically every eventuality under the sun. In their many years of fighting for mutant rights, the X-Men have found themselves in the kind of situations that would test any team, but one thing it seems like they've dealt with more than their fair share of is betrayal. Readers have watched the team and their villains betray everyone in several ways. There are a few things that every reader expects from X-Men comics, and heaping helpings of betrayal are always on the menu.
Source：https://www.cbr.com/x-men-comics-biggest-traitors/
