Sadie Sink spent months remaining tight-lipped about her mysterious role in Spider-Man: Brand New Day — and now that the movie is finally in theaters, it’s easy to see why.

Speculation surrounding who the Stranger Things star would play in the Marvel blockbuster began almost as soon as she was cast in March 2025. The internet was rife with fan theories about her mysterious character, and Sink and her costars repeatedly sidestepped questions about the role.

According to director Destin Daniel Cretton, there was a “very real reason” for keeping the role under wraps. “If people are gonna get mad, I can’t control that! I wish everything was a secret,” he told Rolling Stone in July. “Some people wanna know everything, and some people don’t. There are certain people like me — if I know I’m gonna watch a movie, I try not to even watch the trailers.”

He added, “You’ll see when you watch the movie that there’s a very real reason not to tell people who Sadie Sink is playing. And I don’t think you’ll get mad at it. I think you’ll be like, ‘Oh, I’m glad I didn’t know that.'”

Now that Spider-Man: Brand New Day has been released, audiences finally have their answer.

Warning: This story contains major spoilers for Spider-Man: Brand New Day.

Sadie Sink’s secret ‘Spider-Man’ role

Marvel’s biggest casting secret is finally out: Sink plays Jean Grey, marking the X-Men character’s introduction into the Marvel Cinematic Universe (MCU). The mutant was previously played by Famke Janssen and Sophie Turner in non-MCU movies.

In Brand New Day, Jean is introduced as a young telepath whose life is upended after her older sister, Sara (Olivia Booth-Ford), dies following secret experiments carried out by the Department of Damage Control, the government agency responsible for containing superpowered threats.

Peter Parker (Tom Holland) initially helps the agency capture Jean, believing she is a threat. But after learning the truth about what happened to Sara, he races to stop Jean’s quest for revenge.

Peter ultimately persuades Jean to abandon her plan by sharing a memory of his late Aunt May (Marisa Tomei).

When Frank Castle (Jon Bernthal), the vigilante known as the Punisher, fires a sniper shot at Jean, Peer throws himself into the path of the bullet. Jean uses her powers to keep him alive until he reaches the hospital.

By the end of the film, Jean leaves New York, setting up the next chapter of her story in the MCU.

What’s next for Jean Grey

Sink has confirmed she will reprise her role in Marvel’s X-Men reboot, which will be released in theaters on May 5, 2028. Plot details remain under wraps, but Thunderbolts filmmaker Jake Schreier will direct the film, while Beef creator Lee Sung Jin and The Bear co-creator Joanna Calo are writing the screenplay.

Heartstopper‘s Kit Connor has been cast as Scott Summers, better known as Cyclops, the primary leader of the X-Men. Wolf Man actor Christopher Abbott will appear as Professor Charles Xavier, while Ready or Not star Samara Weaving will play Emma Frost. Obsession‘s Inde Navarrette has joined the movie as Rogue, and Star Wars actor Adam Driver will star as the villainous Nathaniel Milbury.

Speaking to Variety about the character’s next steps, Sink said, “I feel really lucky that I have this introduction through Spider-Man and [her] backstory. I think that’s what X-Men is all about too.

“The more I’ve gotten into it and researched, what makes them special is that they are all incredibly flawed and maybe have done bad things. That makes them more compelling, complex characters and a more complex hero if they don’t start out that way. And they have to find their relationship to their powers.

“Because it’s not like they’ve asked for this or that these strengths make their lives easier; they make them a lot harder, actually. So, knowing Jean’s struggle will be important in the future of her character and where she goes, just makes her really well-rounded, which I’m excited for.”

In a separate interview with Vanity Fair, she said, “I think the timing of it is so exciting, and the way they planned it out is really clever, just with introducing one of the mutants, a very important mutant, through Spider-Man.”

Her comments came after Marvel Studios head Kevin Feige announced that Grey would “play a key role in the future of the MCU,” adding that the character has “immense significance within the Marvel Universe.”

Separately, Schreier has teased that the movie will explore “untold” stories from the comics. “One of the great things about the comics is there is such a rich and broad history,” he told Good Morning America. “That was one of the first things that Kevin and I talked about when I came in; they made many great movies in this world, and they’ve made so many great things. Let’s find the things that haven’t recently been done well. All these other corners of the universe.”

He added, “There are so many stories that are still untold, to honor and to reach into, and then to meet this cast and try to do something new, I think you always want to see something that reveres where it came from and then is still taking a new spin on where we want to go.”