9. According to Bryan Singer, he could only get the film started with confidence once Hugh Jackman and Sirs Patrick Stewart and Ian McKellen agreed to return.
10. Young Xavier tells Logan to "F*** off." This was the original scripted line for Hugh Jackman's cameo in X-Men: First Class (2011); however Jackman instead improvised the "Go f*** yourself" line.
11. This is the sixth time that Patrick Stewart has appeared in an X-Men film; Stewart had made an uncredited appearance in X-Men Origins: Wolverine (2009), and appeared in The Wolverine (2013)'s credits scene. The only X-Men movie he wasn't involved in up to Days of Future Past was X-Men: First Class (2011).
12. According to Peter Dinklage, Bryan Singer picked him to play Bolivar Trask because of his height, stating, "With my dwarfism, I'm a bit of a mutant. I can't move metal or anything, but I thought of it as self-loathing. Deep down, Trask is quite sensitive about that aspect of himself."