One of the biggest surprises in Spider-Man: Brand New Day (2026) stayed hidden until audiences finally saw the movie, and it didn't take long for fans to start looking ahead.
Sadie Sink's mystery role has officially been revealed as Jean Grey, introducing one of Marvel's most recognizable mutants into the MCU. While the film answers one major question, it leaves another unanswered: where will Jean appear next?
Marvel hasn't announced Sink's next appearance, but the movie's ending has already sparked theories. With an X-Men reboot expected in the coming years and another Deadpool movie widely rumored, fans are already wondering where Jean could fit into the MCU's future.
Jean Grey Makes Her MCU Debut
Instead of tying Jean Grey (Sadie Sink) directly to the X-Men from the beginning, Spider-Man: Brand New Day introduces her through a personal conflict.
Damage Control kidnaps Jean's older sister, Sara Grey, and begins experimenting on her. Determined to save her sister, Jean launches an attack against the organization, putting her on a collision course with Peter Parker/Spider-Man (Tom Holland).
Peter doesn't know the full story at first. Believing Jean is responsible for the violence, he turns her over to Damage Control. Once he learns what happened to Sara, however, he changes course. Peter helps Jean escape, and the two eventually join forces to stop Damage Control's plans.
After helping Peter, Jean leaves on her own. Her final scene shows her riding a bus toward an unknown destination, giving Marvel plenty of room to continue her story later.
Fans Think the Ending Could Point Toward the X-Men
Marvel never reveals where Jean is headed, but that hasn't stopped fans from forming theories.
One of the most popular ideas is that she's traveling to Charles Xavier's School for Gifted Youngsters. The movie never confirms that destination, yet the ending feels intentionally open-ended.
That has become even more interesting because Marvel has not officially announced Sink as part of Avengers: Doomsday. Meanwhile, the studio has confirmed the return of Cyclops (James Marsden), Magneto (Ian McKellen), and Mystique (Rebecca Romijn) from Fox's X-Men films.
Notably, Jean Grey, Storm, and Rogue have not been included in those announcements.
Marvel is known for keeping major surprises under wraps, so additional casting announcements could always come later. Still, some fans believe the current lineup suggests Avengers: Doomsday may focus on legacy mutants while Marvel saves a younger generation for its eventual X-Men reboot.
A New Generation of Mutants May Be Coming
Another detail that stands out is Jean's age.
Sink's version of the character is portrayed as a teenager, suggesting that Marvel could be building a younger roster of mutants rather than simply replacing the Fox-era versions with older actors.
That possibility has fueled speculation about other familiar names. Ryan Coogler has supposedly been involved in casting Storm for the MCU, leading some fans to wonder if she could first appear in Black Panther 3. Rogue's debut remains a mystery, although others have suggested she could appear in a future Deadpool movie before eventually joining the X-Men.
Marvel has confirmed none of those ideas, but introducing mutants gradually across multiple projects would give each character time to develop before the team officially assembles.
Could Deadpool Help Introduce More Mutants?
A future Deadpool movie could also provide another opportunity to expand Marvel's mutant lineup.
Wade Wilson/Deadpool (Ryan Reynolds) has already shared the spotlight with younger characters. Firefist (Julian Dennison) became an important part of Deadpool 2 (2018), while Laura Kinney/X-23 (Dafne Keen) played a memorable role in Deadpool & Wolverine (2024).
Because of that history, some fans believe Jean or other young mutants could appear alongside Deadpool before receiving larger roles elsewhere. Others think Marvel may simply use brief cameos to continue setting up the franchise.
There is no official evidence linking Sink to another Deadpool movie, but the theory has become a popular one among fans.
Waiting to See What's Next
For now, Marvel has only confirmed one thing: Sadie Sink is Jean Grey.
The studio has not announced her involvement in Avengers: Doomsday, Avengers: Secret Wars, or the upcoming X-Men movie. Of course, Marvel has built its reputation on protecting major surprises, so future appearances can't be ruled out.
At the moment, Jean's future remains one of the MCU's biggest unanswered questions. Whether her next stop is Charles Xavier's school, a future Deadpool adventure, or Marvel's eventual X-Men reboot, fans have plenty of reasons to keep watching.
