SPOILER ALERT: Do not read if you have not yet watched Season 1, Episode 5 of Disney Plus’ “WandaVision.”

As Marvel Studios ventures further into its new adventure in episodic television with “WandaVision,” it’s been fascinating to watch fans digest an MCU project as it’s still unfolding. Every new twist spawns its own small ecosystem of Twitter excitement, YouTube easter egg hunts, and feverish online speculation about what it all means.

That leaped to a new frenzied peak in the latest episode with the shocking reveal that Pietro Maximoff — the dearly departed brother of Wanda Maximoff (Elizabeth Olsen) — has come back from the dead. But the actor playing him isn’t Aaron Taylor-Johnson, who originated the role in “Avengers: Age of Ultron.” Instead, it was Evan Peters, who played Peter Maximoff in three “X-Men” movies that were not part of the Marvel Cinematic Universe.

It’s the kind of head-squeezer designed to launch a thousand fan theories about What It Could All Mean: Is the MCU diving head first into the multiverse? After Disney’s purchase of 20th Century Fox in 2019, does this mean all the “X-Men” movies are getting retconned into the MCU? Is Peters playing some other version of Quicksilver from some other alternative reality?

Most crucially: With four more episodes to go, who else could show up in the wacky world of Westview, New Jersey?

Evans’ casting at least seemed to resolve one mystery that had tantalized fans all week: The identity of a mysterious — and, according to Olsen and Paul Bettany, mind-blowing — upcoming character.

Or…did it?

Here’s what we know for sure: In a Jan. 26 interview with Variety‘s sister outlet IndieWire, Bettany said that he was surprised that an actor’s upcoming role on the show hadn’t yet been leaked.

“So many things get leaked, but there’s this thing that has been completely under wrap that happens,” Bettany said. “I work with this actor that I’ve always wanted to work with and we have fireworks together, the scenes are great and I think people are going to be really excited. I’ve always wanted to work with this guy and the scenes are pretty intense.”

So to recap: It’s an actor, probably male, who Bettany says he hasn’t worked with before, but has enough stature in the industry to make Bettany yearn to be able to work with him.

Then on Feb. 2, Variety sister publication TV Line dropped an even more cryptic interview with Olsen. After the story first alluded to the bombshell appearance of a de-aged Mark Hamill as Luke Skywalker in the Season 2 finale of “The Mandalorian,” Olsen was asked if anything similar is in store on “WandaVision” — namely, a big cameo that no one knows is coming.

Olsen’s reply: “Yes.” And then: “I’m really excited.” And that was it!

Those two interviews — and the mistaken impression that Olsen herself said the cameo was on par with Luke Skywalker’s return — got fans wildly speculating as to who could possibly live up to these wildly imprecise expectations.

And perhaps Peters fits the bill. He certainly hasn’t worked with Bettany before. But as talented as Peters is, at 34 years old, it doesn’t quite seem like he’s who the 49-year-old Bettany would have “always” wanted to work with. Besides, if one former “X-Men” actor can reprise his role on “WandaVision,” a whole pandora’s box of possibilities has suddenly been blown wide open.

So what other big cameos could be in store “WandaVision”? Let’s look at the likeliest — and less than likely – candidates.