X-Men: Apocalypse's post-credits scene is a quick tease of what might be next for the series

If you stick around through the (lengthy) end credits of (the even lengthier) X-Men: Apocalypse, you'll be treated to a comparatively short surprise at the very end. That's typical for Marvel movies, even those produced by 20th Century Fox (as the X-Men series is). But considering X-Men: Apocalypse is meant to conclude director Bryan Singer's trilogy, it's interesting that the final clip doesn't serve as a clean epilogue.

Instead, the post-credits scene teases what's coming next for the X-Men movie universe. X-Men: Days of Future Past ended with the introduction of its sequel's villain, Apocalypse — but what's going on in X-Men: Apocalypse's last moments?

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X-Men fans might pick up on it, but to the layman or anyone less well-versed, here's a quick rundown.

Spoilers, obviously, will follow from this point forward.

First, the scene itself: We return to Major William Stryker's lab facility, from where the mutants escaped earlier in the film after they're captured by the villainous scientist. They hadn't made a clean break, though; the X-Men only managed to escape thanks to some brutal, bloody help from Wolverine, Stryker's prized prison experiment.

So now we see a cleaning crew doing their best to fix up the facility, clearing out the dead bodies and wiping up the blood. But they're not alone: A mysterious man enters, walking through the building in search of something. That happens to be a vial of blood labeled "Weapon X," which he adds to his collection. His various vials are held in a briefcase that bears the name Essex Corp.

Although it's not explicit, fans at our screening of Apocalypse got excited by what they saw as a reveal that Nathaniel Essex, otherwise known as Mister Sinister, would be the next X-Men villain to appear on-screen. The popular supervillain is a scientific mastermind, a British businessman with a fondness for evolution.

He also is a genetically modified, shape-shifting, ageless telepath, becoming that way thanks to ... well, Apocalypse, funnily enough. In the comics, a power-mad Essex teams up with Apocalypse in order to further his scientific research during the 1800s; after losing his child and wife, though, Essex turns to Apocalypse, bitter and lost. Apocalypse imbues the scientist with the powers of telekinesis and regeneration and orders him to help destroy the world — creating Mister Sinister.

Sinister becomes one of the X-Men's greatest foes, but he's yet to make it to the big screen. Considering he doesn't factor into the plot of X-Men: Apocalypse, which ends with the defeat of the titular villain, it's unclear how his backstory would play out in a future film. That Essex is picking up blood from William Stryker's lab, though, suggests he'll have a presence in a future X-Men movie — like the upcoming, final Wolverine sequel.

Stryker has long had his eye on the hero, and in X-Men: Apocalypse, the Major's had him locked up for experiments for who knows how long. Last month, actors for the third Wolverine were cast in the roles of an Essex Corporation employee as well as a "mad scientist."

We don't know where Wolverine heads off to after his Apocalypse cameo, but now that Essex has what is very likely his blood, it makes sense that he'll soon be on the mutant's trail.

The third Wolverine film hits theaters March 3, 2017. Star Hugh Jackman has said it will be his last turn as the character, whom he's portrayed since the first X-Men, which premiered in 2000. There are more X-Men movies on the way, like the spinoff New Mutants; Bryan Singer also reportedly wants to take the series into outer space in a future installment. The X-Men are also coming back to TV in Legion, now in production at cable channel FX.