SPOILERS are ahead for Spider-Man: Brand New Day! Go see the movie in theaters. Sadie Sink just completely changed what’s next in the MCU. After over a year of anticipation, it was revealed in Spider-Man: Brand New Day that the 24-year-old Stranger Things alum is the MCU’s Jean Grey. Now that the cat’s officially out of the bag, Sink just talked about who she told her confidential casting to (and that list includes some surprising folks from Stranger Things). Being a mutant is not an easy secret to keep, but Sadie Sink seemed to do an incredible job staying tight-lipped. But in a new interview, she just shared how many people she told about the mysterious role. In her words: I mean, it was definitely more than three, if I’m being honest. You have people that you can trust within the industry to talk about it. So, my family knew and everything, and then I slowly … like the Duffers were some of the first few people I told. Because I was filming with them, and they’re obviously huge influences in my career and life, and have watched me grow up, so I wanted them to know that that’s what I would be doing next. And they were so excited.In an interview with Variety, Sadie Sink admitted that she had a handful of trusted confidants outside of Brand New Day. The actress said she told members of her family and the creators of Stranger Things, Matt and Ross Duffer, were in the know too, which kind of surprised me. Here’s what she said of the Duffers’ reaction to the big MCU role: Well, they were just like, ‘That’s the best character. You have to do it!’ and like, ‘That’s perfect. You’re going to be amazing,’ and blah blah blah. They thought it was the right fit for me, and I trust their opinion because they love comics and stuff like that, and are very well versed with these characters, so it was good to have their input.Sadie Sink admittedly knew very little about Jean Grey and had never seen the X-Men movies when she was approached for the Brand New Day role. It sounds like their reaction to the opportunity really helped give her confidence to take it on, especially since the Stranger Things creators are comic book fans themselves. But did she tell any of her Stranger Things cast? As she responded: I didn’t really tell anybody else [from Stranger Things]. That was kind of it.Whoa. I guess her castmates were left in the dark for the past year and some change after she was picked to be Jean Grey. There’s been a ton of rumors surrounding who Sink was playing (including her actual role being leaked early on). Since she was cast in March 2025, Sadie has had to find unique ways to tease her role without revealing it. As a result of all the hush-hush, there were big reactions in theaters at her character being named in Brand New Day. If I were one of Sadie Sink’s castmates, I would have probably tried to get the tea – so I’m shocked to learn only the Duffers were clued in among the Stranger Things family. Now that Sadie Sink’s Jean Grey has been introduced in Brand New Day, she’s expected to be in the planned X-Men reboot. Of course, she could share the secret to her Brand New Day family (who she once made feel old), or she could confide in the Duffers again. However, no matter what happens next, now that Brand New Day has had the biggest box office week ever and soared to over $1 billion worldwide, it's safe to say a lot of people know Sadie Sink’s character now!