Sadie Sink kept her major Marvel Cinematic Universe casting secret hidden from almost the entire Stranger Things cast for nearly two years—with Stranger Things creators Matt and Ross Duffer being among the very few people she trusted with the news during the filming of the final season.

Trusting the Duffer Brothers

Sink revealed that she felt compelled to share the milestone with the Duffer brothers, citing their instrumental role in her personal life and career as she grew up on the show’s set. Upon hearing the news, their encouragement was immediate: they told her that Jean Grey was the perfect role for her and insisted she take it.

A Two-Year Marvel Secret Revealed

Outside of the show’s creators, Sink maintained strict secrecy, keeping the news under wraps until her official reveal as the MCU’s Jean Grey in Spider-Man: Brand New Day.

Transitioning from her breakout role as Max Mayfield in Hawkins to one of the most iconic mutants in Marvel lore, Sink’s milestone brings her journey full circle—with the creators who guided her rise being among the first to witness her next massive chapter.