With weeks to go until its finale, the Disney+ series WandaVision may have already radically altered the entire Marvel Cinematic Universe.

The show dropped a massive bombshell in Friday's episode when, in the final scene, (spoiler alert!) a character we're meant to believe is Wanda's late brother Pietro shows up. But here's the twist: He's played not by Aaron Taylor-Johnson, who played the character in prior MCU films, but by Evan Peters. It's hard to overstate just how big a deal this is, and depending on how the moment is interpreted, it could have massive implications for the Marvel franchise.

To explain why requires a bit of context. When Marvel Studios launched its cinematic universe with Iron Man, it notably lacked the film rights to some major characters and storylines from the comics. Namely, the X-Men, who were owned by 20th Century Fox and already starring in their own films featuring Patrick Stewart and Ian McKellen, were off-limits. As a result, when the MCU brought Wanda Maximoff and her twin brother Pietro (a.k.a. Quicksilver) to screen in Avengers: Age of Ultron, their backstories were tweaked to remove any X-Men elements, including Magneto being their father. Meanwhile, the X-Men films separately introduced their own Quicksilver in Days of Future Past, so we had the MCU version of Quicksilver played by Aaron Taylor-Johnson in Avengers, plus a totally different version played by Evan Peters in the non-MCU X-Men movies.

But all of this was prior to Disney purchasing 21st Century Fox in 2019. At that point, Disney — and, in turn, Marvel Studios — regained all the X-Men rights, not to mention the rights to the previous X-Men films and its spinoffs made under Fox. But the question remained, what was to come of these movies and their characters? The common assumption was that, with the exception of the Deadpool films, they would basically be ignored, and Marvel would eventually introduce the X-Men fresh as if no previous movie version existed. After all, that was the approach they took when introducing Spider-Man into the MCU following an arrangement with Sony.

That's why it's so significant when, in Friday's WandaVision, Quicksilver makes an appearance and is bizarrely not the Aaron Taylor-Johnson version but the Evan Peters version.

One way to interpret the scene is that this is Marvel's first major step toward exploring the idea of a multiverse, and thus bringing characters and storylines from outside the MCU into the mix to dramatically expand its world. Peters' version of Quicksilver may have actually crossed fictional universes and arrived straight from the Fox world into the MCU world. How did that happen? Well, the show has been suggesting Wanda is in control of what's occurring in Westview, and earlier in Friday's episode, she told her kids all about how sad she is that her brother is "far away from here." Perhaps she attempted to bring him back, either consciously or subconsciously, only to somehow bring back the version of him from another universe.

Of course, there are some other possible interpretations. It could be our takeaway is simply meant to be that Quicksilver for some reason looks different, perhaps as a meta comment on sitcoms recasting actors, hence Darcy's question, "Did she recast Pietro?" In this scenario, it's possible the use of Peters is only meant to be an in-joke for fans of the Fox films. Maybe he could just be a random town resident who's now under Wanda's spell like everyone else, and not actually the same character Peters played. One would think, though, that the implications of using Peters himself are too monumental for a mere meta joke.

Then again, Wanda looks surprised to see Pietro, and she claims she isn't responsible for his doorbell ring, so a third interpretation is that this character actually isn't either version of Quicksilver, but instead Mephisto in disguise. In the comics, Mephisto is essentially Marvel's version of the devil, and WandaVision fans for weeks have speculated he could secretly be behind everything in Westview. But if Mephisto were to disguise himself as Wanda's brother for the purpose of tricking her, surely he'd do so as the version she's familiar with, right?

There are other reasons to think this Quicksilver really could be straight out of the Fox universe. For one, prior to WandaVision, it's already appeared that Marvel was getting ready to explore the multiverse in its future films. WandaVision is meant to set up the events of Doctor Strange's upcoming sequel, which is titled Doctor Strange in the Multiverse of Madness and will actually have Wanda in it. We also know the next Spider-Man movie will be bringing back actors from the non-MCU Sony universe of Spider-Man films, including Jamie Foxx and Alfred Molina, with rumors suggesting Tobey Maguire and Andrew Garfield could even return as their versions of Spider-Man.

So could all this multiverse madness that's apparently on the way start here, as a result of Wanda's desire to be reunited with her brother? Could dealing with the aftermath of Wanda, or someone else like Mephisto, opening up another universe be the whole plot of the next Doctor Strange?

If that's the case, the driving force of the MCU for at least the next year or so may have just been unlocked. Even more importantly, this has major implications for the future of the X-Men, suggesting the plan might not be to fully wipe the slate clean like we thought, but actually fold elements of their old universe into the MCU. Peters' appearance at least establishes a willingness on Marvel's part to acknowledge the existence of the movies that weren't made by them. Could that suggest Patrick Stewart's Charles Xavier, or even Hugh Jackman's Wolverine, might one day show up in some massive Avengers event film?

There's quite a lot to chew on just from one cameo. So much for complaints that this show is uneventful, huh?