Ever since Sadie Sink joined the cast of Spider-Man: Brand New Day, her role has remained a closely guarded secret. But you’ll see when you watch the movie that there’s a very real reason not to tell people who Sadie Sink is playing. Who does Sadie Sink play in Spider-Man: Brand New Day? I like her character,” Lacy revealed. “Sadie Sink is Jean Grey, and she delivers one of the film’s strongest performances alongside Holland,” they wrote.