The internet is abuzz on Monday over the drop of the Deadpool & Wolverine trailer, with its blockbuster MCU pairing of the two beloved Marvel superheroes, though it's the film's villain — The Crown star Emma Corrin as Cassandra Nova — who seems to be getting the lion's share of social media reactions.

Corrin, who identifies as non-binary, is most famous for portraying Princess Lady Diana Spencer in Season 4 of the Netflix fan-favorite The Crown, for which they earned Golden Globe and Critics Choice awards.

Now, they're entering the vaunted MCU in a supervillain role that's stunning some longtime Marvel Comics fans.

“Even 25 years after the first X-Men I can't quite believe they've really put Cassandra Nova in a movie that regular people are going to go watch,” posted one X/Twitter user.

That seems to be the prevailing sentiment online, with Nova viewed as a highly complex, complicated and fascinating supervillain in the comics. First introduced in New X-Men #114 in July 2001, Nova has a slew of extraordinary abilities — such as telepathy, psionic powers, and a penchant for destruction and mass murder.

So who is Cassandra Nova in the MCU?

Nova is the yin to Dr. Charles Xavier's yang — his polar evil opposite. In the comics, Nova is often referred to as Xavier's twin sister — since she, being born without a body, decided to clone Xavier's DNA to give herself a material form, then became convinced her mission was to destroy Xavier and everything he holds dear.

Long story short, Cassandra Nova helps put your own dysfunctional family issues into perspective, and MCU fans seem particularly excited about watching Emma Corrin take on the role.

Another post declared, “Here’s what you gotta know about Cassandra Nova: She’s Clever. She’s Sadistic. She’s got a very dark sense of humor. She’s very f—ing dangerous. She will not hesitate to kill your fav. She’s a very real threat to the Multiverse.”

One of the highlights of the new trailer is a battle between Wolverine and Nova in which she manipulates his body movements to make Wolverine stab himself with his own claws.

As one excited commenter noted, “Wolverine's claws vs Cassandra Nova's cunning in ‘DEADPOOL & WOLVERINE'—it's like watching a knife fight with a shape-shifter!”

Another post read, “Cassandra Nova looks so cool I’m really excited to see Emma’s take on her, she’s such a weird character (complimentary) who I never thought we’d see in live action.”

Nova's living quarters revealed in the trailer also generated a lot of excitement online, with one post exclaiming, “Charles Xaivers sister, Cassandra Nova is using a f—ing Antman skull as her base!”

Indeed she is, though why that's her headquarters remains to be answered.

One thing that is clear from the Deadpool & Wolverine trailer — MCU fans are fired up about Emma Corrin taking on the role of Cassandra Nova and are taking to social media in droves to vociferously share their thoughts. If Marvel Studios is going to turn their recent lackluster fortunes around, it sure seems like this film is their best hope.