'WandaVision' had a jaw-dropping reveal that both overjoyed and confused fans. Here's what's going on.

• Warning: There are massive spoilers ahead for episode five of "WandaVision."
• The very end of the episode shows an appearance by an X-Men actor.
• Fans are excited and confused. How is this possible? What does it mean for the MCU? We'll explain.

Friday's "WandaVision" ended with a jaw-dropping reveal that may alter the Marvel Cinematic Universe forever.

The show brought back Wanda's brother, Pietro, who died in 2015's "Avengers: Age of Ultron." But the person who rang Wanda's doorbell at the episode's end wasn't the Pietro we remember.

Instead, Evan Peters, who played fan-favorite Quicksilver in the "X-Men" movies, greeted Wanda, asking for a hug from his sister.

Fans were floored.

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If you're confused by what's going on and why fans are so overjoyed by this character's appearance, here's a quick recap.

Aaron Taylor-Johnson played one version of Quicksilver in Marvel's "Age of Ultron." Simultaneously, Evan Peters was starring in Fox's "X-Men: Days of Future Past" as a different version of the same character.

At the time, the two franchises were owned by competing movie studios. Disney/Marvel weren't allowed to have X-Men or use the word mutants. (Here's a handy explainer breaking that down a bit more.)

Read more: Why Quicksilver was allowed to appear in "Avengers: Age of Ultron" and "X-Men" movies

Peters' "X-Men" version of the character became a break-out favorite among fans.

Honestly, it's not tough to see why when you watch this scene:

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In 2019, Disney acquired Fox's film and TV properties. Now, they have the rights to characters, including Deadpool, the X-Men, and Peters' Quicksilver.

Now that you're up to speed, "WandaVision" took advantage of a known sitcom and soap opera trope and cleverly "recast the role" of Pietro in order to explain away how and why Peters was now playing the role.

But there's likely more going on.

Is this really the 'X-Men' Quicksilver we know or is something else going on?

Once past the shock and joy of seeing the "X-Men" character seemingly cross over onto a Disney property, fans are starting to have a lot of questions and suspicions.

Here are a few of them:

• Did Wanda just bring her dead brother back to life in the way she apparently brought Vision back to life? (It sure seems that way, but we're skeptical.)
• Is the MCU bringing the X-Men into the fold? (We hope! But it may be too soon.)
• Is that even really the X-Men Quicksilver fans love or is he some conjured up vision to placate Wanda? (Can't we just let Wanda be happy?)
• Is there something else more nefarious going on behind the scenes? (Likely.)

The answer to most of these may be connected to that final question. While Wanda has created her own happy alternate reality in Westview, some fans have theories there may be another villainous character, Mephisto, pulling some of the strings and toying with Wanda.

Read more: The 15 biggest questions we still have about Marvel's 'WandaVision'

That theory may not be far off. At the end of Friday's episode, even Wanda seemed completely shocked to see a version of her brother standing in front of her. She audibly gasps and asks the man if he really is Pietro.

Even if Wanda has been acting on her own sitcom, she may not be that good of an actress.

Has Wanda broken the multiverse? We'll have to wait until next week for more clues as to what's really going on in Westview.