The Marvel Cinematic Universe has been around for nearly two decades and is a well-oiled machine at this point. Fans are consistently treated to new content, both in theaters and streaming with a Disney+ subscription. The next highly anticipated upcoming Marvel movie heading to theaters is Spider-Man: Brand New Day, with fans still in the dark about who Sadie Sink is playing. And Tom Holland's comments about her performance are making the wait even worse. Sink was noticeably missing from the Spider-Man: Brand New Day trailer, but that hasn't stopped the discourse from swirling around her role. During an interview with Collider, Holland complimented how great the Stranger Things star is in the blockbuster, offering: There’s two moments. There’s one with Sadie Sink, who’s making her MCU debut. She handled the pressure of the character that she’s playing with such grace, and the third act, she steals the movie. It is so good.As if I wasn't already invested in finding out who Sink is playing. It sounds like she really gets her chance to shine in Brand New Day's third act, and might even steal the whole movie. Considering how much time and work Tom Holland put into playing the title role, his comments are especially noteworthy. And I need this movie to arrive in theaters yesterday. So who exactly will Sadie Sink be playing in Destin Daniel Cretton's forthcoming Spider-Man sequel? It's currently unclear, but the most popular fan choice is Jean Grey. Since the X-Men are finally joining the MCU, folks think that the new cast might be slowly introduced, starting with Jean. (Image credit: Netflix)Fans who spent years watching the Marvel movies in order have been waiting for the X-Men to join the shared universe, and Disney's acquisition of 20th Century Fox finally opened the door for this to happen. But while the OG stars of the X-Men movies will appear in Avengers: Doomsday, a new cast of mutants will be assembled for Jake Schreier's developing X-Men movie. We'll just have to see if Sadie Sink is actually playing Jean Grey, or if she ends up being one of the other rumored characters. Other names being tossed around online include Punisher sidekick Rachel Cole, a variant of Mary Jane Watson, Teresa Parker or even a variant of Wanda Maximoff.Our answers will come when Spider-Man: Brand New Day hits theaters on July 31st as part of the 2026 movie release list. There are just a few weeks left, so we'll have to see if the studio can keep the movie's secrets under wraps until then. Thank goodness answers are finally coming later this month. Producer Amy Pascal has talked the importance of the movie's secrecy, and so far it's been largely spoiler-free.