“I’m a terrible liar… I guess you become good at lying. But honestly, I’m really bad at lying. The entire appearance was so hush hush. It was like, ‘We have to find a way of getting you to the airport with no one seeing you.'” Movie bosses went to great lengths to keep Famke Janssen’s cameo appearance in X-Men: Days Of Future Past a secret. Janssen plays Jean Grey in the mutant franchise.