The following post contains SPOILERS for WandaVision Episode 5.

This week’s WandaVision is titled “On a Very Special Episode...” and while it and every Wandavision episode title is a reference to old TV lingo (last week was “We Interrupt This Program”), that was also quite accurate. Most of the episode continued the show’s parallel storylines; Wanda carrying on her phony sitcom life inside the town of Westview, Monica Rambeau and the agents of S.W.O.R.D. investigating the “anomaly” from outside the energy barrier protecting it from the rest of the world.

Then that cameo arrived. Just as Vision (Paul Bettany) made sense of the wrongness of his life with Wanda (Elizabeth Olsen) and their two magical children, there was a knock on their front door. Wanda opens it in and is dumbstruck to see her long-lost (technically long-dead) brother Pietro standing at her door.

Only it’s not her Pietro.

Marvel

It’s Evan Peters, the Quicksilver of Fox’s X-Men franchise. Peters played the character three times: In X-Men: Days of Future PastX-Men: Apocalypse, and Dark Phoenix. Because Fox controlled the movie rights to the X-Men universe (where both Pietro and Wanda were first introduced in the pages of 1964’s The X-Men #4) while Marvel controlled the Avengers film franchise (where Pietro and Wanda were longstanding members of the team) the character appeared nearly simultaneously in two different versions. In the X-Men movies, Evan Peters’ “Peter” lives a quiet life in the American suburbs until he’s recruited for a special mission by Professor Xavier. In the Marvel Cinematic Universe, Aaron Taylor-Johnson’s Pietro Maximoff initially helps Ultron in his attempt to conquer the world, then turns on him to help the Avengers. In the ensuing battle, Pietro dies saving Hawkeye from a hail of bullets.

Pietro and Peter look basically the same, and they have the same powers of super-speed. Their origins, though, are different. Peters’ Peter is Magneto’s illegitimate child, born in America. Taylor-Johnson’s Pietro and his sister are orphans from the European nation of Sokovia, where the death of their parents radicalized them. More importantly, Fox’s X-Men movies and Marvel’s cinematic universe had never crossed paths... until this scene. Which makes this an absolutely gigantic moment in the history of the MCU.

Marvel

It’s possible that this is just very clever stunt casting on Marvel’s part. As Pietro’s shocking return unfolds on the WandaVision show-within-a-show, Darcy Lewis mutters “She recast Pietro?” It’s possible that Peters isn’t playing the version of Quicksilver seen in those three X-Men movies. He could be playing one of many residents of Westview trapped inside the town — this week’s episode establishes that “thousands” of people in the area have been affected by Wanda’s powers. In the same way that Vision’s co-worker Norm (Asif Ali) is a guy forced by Wanda’s powers to play a role different form his real life, this Pietro could actually be some schmoe from down the street manipulated into maintaining this illusion because of his physical resemblance to Wanda’s brother. (On a related note, the episode did an outstanding joke of teasing this moment out, introducing Peters from behind so that only his hair is visible, making the audience briefly think that it was Taylor-Johnson’s Pietro who’d returned.)

That would be way out of Marvel’s style though. The company pays incredibly close attention to matters of continuity like this — and they know their fans do too. They know what it means to have an actor from the Fox X-Men movies show up in the MCU: It’s the first step in combining Fox’s X-Men and Marvel’s MCU universes into a shared reality.

It’s also one that makes a lot of sense in this context, because we know that Wanda will next be seen in Doctor Strange and the Multiverse of Madness, the upcoming sequel whose title promises to reveal how the Marvel Cinematic Universe connects to an entire multiverse of alternate realities. With that in mind, it seems very possible that this Quicksilver is the same one from those X-Men movies, plucked by Wanda (or whoever seems to be controlling her) out of his reality and brought to this one because the MCU’s Pietro is really dead.

Then again, Vision is supposed to be dead too? There are still a lot of mysteries that need to be resolved in the final four episodes of this show. The longer WandaVision goes on, the more it seems like the answers to our questions will legitimately alter the course of the MCU forever. If Evan Peters’ Quicksilver can show up, who else might knock on Wanda’s door next week?

New episodes of Wandavision premiere on Fridays on Disney+.

Gallery — Our Favorite WandaVision Easter Eggs So Far: