The Marvel Cinematic Universe loves a good secret, and one of its best-kept mysteries just became even more intriguing. Sadie Sink, whose character in the upcoming “Spider-Man: Brand New Day” remains firmly under wraps, will reportedly reprise that role in 2027’s “Avengers: Secret Wars,” according to Deadline.
The “Stranger Things” star is expected to begin filming the massive Avengers blockbuster later in 2026, following her appearance in next summer’s Spider-Man installment. Notably, there’s no indication that Sink will appear in “Avengers: Doomsday,” the first of the two-part Avengers finale that precedes “Secret Wars.”
The Mystery Deepens
Marvel Studios has maintained absolute secrecy around Sink’s character, refusing to confirm or deny the swirling speculation about who she’s playing. This strategic silence has only intensified fan debate, with theories ranging from iconic X-Men heroes to cosmic villains to characters with deep personal connections to Spider-Man’s multiverse.
The news that Sink will return for “Secret Wars” has significantly narrowed the speculation. If her character is important enough to carry over into the MCU’s multiversal grand finale, she’s likely playing someone with major implications for the larger Marvel universe—not just a one-off love interest or minor antagonist.
The Leading Theories
Fan communities have coalesced around several strong candidates for Sink’s mysterious role:
Mayday Parker – Perhaps the most popular theory, especially following today’s news. Mayday is the daughter of Peter Parker and Mary Jane Watson in the comics’ MC2 universe. The twist that has fans most excited? The speculation that she could be the daughter of Tobey Maguire’s Spider-Man, providing a emotional throughline that connects the Multiverse Saga to the beloved Sam Raimi trilogy. Maguire’s potential return for one final appearance to close out this era would make this reveal particularly powerful.
Jean Grey – With the X-Men gradually being integrated into the MCU, some believe Sink could be playing a young Jean Grey, one of Marvel’s most iconic mutants and a central figure in many universe-spanning stories.
Shathra – This cosmic spider-deity villain from the comics would certainly justify an appearance in both a Spider-Man film and “Secret Wars.” Shathra represents an existential threat tied to Spider-Man’s very nature.
Rachel Cole-Alves – A lesser-known character who served as a Punisher ally, though this seems less likely given the character’s lack of obvious connections to multiversal storytelling. There even have been some photos of her on set in camo pants, which is a part of this character’s attire. She also could’ve just been wearing camo pants in general.
A Hidden Identity Throughout ‘Brand New Day’?
Many fans believe Sink’s true identity will be concealed throughout much of “Spider-Man: Brand New Day,” with her character operating under an assumed name or secret identity that Peter Parker—and the audience—only discovers as the story unfolds.
“100% Mayday Parker or Firestar,” wrote Marvel fan HLumin on Reddit. “It’s come to those two for me. I’m leaning more towards Mayday. Whoever she ends up being, we will not know until the post credit scene of BND. She will be someone else throughout the movie is my guess.”
This approach would mirror “Spider-Man: Homecoming,” which famously kept Zendaya’s true character identity ambiguous before eventually revealing she was playing MJ—a reimagined version of Mary Jane Watson.
“Mayday makes the most sense at this point,” added Reddit user Puzzled_Influence895. “She shows up as an unassuming side character like ‘Carlie Cooper’, helps Peter out… then drops the hammer and reveals the Tobey connection at the end, which brings him into the multiversal stuff.”
Why Mayday Parker Makes Sense
The Mayday theory has gained significant traction for several compelling reasons:
First, her presence would provide an emotional anchor for the multiverse storyline, giving personal stakes to what could otherwise be an overwhelming cosmic narrative. Discovering that Spider-Man has a daughter in another universe—particularly one who might be facing danger—creates immediate drama.
Second, bringing back Tobey Maguire’s Spider-Man would satisfy fans who’ve been clamoring for more from the actor who defined the character for an entire generation. “Spider-Man: No Way Home” proved the power of multiverse nostalgia, and Maguire’s Peter Parker meeting his adult daughter would be an undeniably powerful moment.
Third, Mayday Parker is a beloved character in her own right, having starred in her own “Spider-Girl” comic series. Introducing her to the MCU could open doors for future stories while honoring Marvel’s comic book legacy.
Finally, the timing works narratively. If Peter discovers Mayday’s identity at the end of “Brand New Day,” it provides the perfect motivation for him to become involved in the multiversal crisis of “Secret Wars”—protecting his alternate-universe niece or even mentoring his counterpart’s daughter.
Marvel’s Masterful Misdirection
Marvel Studios has become legendary for its ability to keep secrets in an age when spoilers spread instantly online. From hiding the true nature of the Mandarin in “Iron Man 3” to concealing Spider-Man’s role in “Captain America: Civil War,” the studio knows how to play the long game with character reveals.
The fact that Sink’s identity has remained secret this long—especially with filming already underway or completed—demonstrates Marvel’s continued commitment to preserving the theatrical experience of genuine surprise.
The Long Wait for Answers
Whether fans’ theories prove correct or Marvel has something entirely unexpected planned, we likely won’t know for certain until “Spider-Man: Brand New Day” hits theaters on July 31, 2026. That’s still over a year and a half away, giving the speculation machine plenty of time to generate new theories.
And if Marvel really wants to test our patience, they could wait until “Avengers: Secret Wars” on December 17, 2027, to fully reveal the significance of Sink’s character. Here’s hoping they show mercy and give us answers before then.
One thing is certain: Sadie Sink has landed herself in the middle of one of the MCU’s most intriguing mysteries, and her performance—whoever she’s playing—will be crucial to the next phase of Marvel’s interconnected storytelling.
