The first trailer has been released for the Arrowverse crossover Elseworlds, and it features a very unexpected pairing. The crossover has become a highly anticipated yearly TV event, including the four TV shows in various combinations (this year Legends of Tomorrow will be sitting out). The crossover this year has the extra pressure of introducing Ruby Rose's Batwoman and Gotham City to the Arrowverse for the first time.

In the comics, the Elseworlds imprint is set outside of the DC continuity. Anything that happens in these stories does not have an impact on the character's current storylines. Which means (even more than usual) that anything can happen. So far it's unclear just exactly how much the crossover will affect the Arrowverse, but it will serve as a set up for a Batwoman TV show. So far, set photos and images shared by the cast have already revealed a number of surprises, from black suited Superman to John Wesley Shipp back in his iconic 1990s Flash suit.

Related: Every Reveal From The Arrowverse Elseworlds Crossover Set Photos

The first trailer for Elseworlds shows the familiar West-Allen apartment - with a twist. Rather than Grant Gustin as the Scarlet Speedster, it's Stephen Amell aka the Green Arrow. However, Iris doesn't seem to know that this man isn't her Barry Allen. She kisses him and then calls him Barry, revealing that everything is definitely not what it seems in this universe. You can watch the trailer below, courtesy of The CW.

Based on the poster for the crossover, fans knew that Amell would don the Flash suit and Gustin would take up the green hood, but now it appears that more than just the costumes have changed. Iris believes that this is her Barry, despite Oliver seemingly knowing otherwise. One can only imagine the reverse happening in Star City, as a confused Barry wakes up next to Felicity. It's bound to make for some pretty hilarious moments between the two characters - like making up for all the times when Barry forgets Oliver isn't as fast as him.

Besides dealing with their own version of Freaky Friday, the Arrowverse heroes will also be facing a dangerous foe in Dr. John Deegan. Played by Jeremy Davies, he's an Arkham Asylum doctor who's described as just as unhinged as his patients. His presence, alongside that of Cassandra Jean Amell as the wife of Mr. Freeze shows how much importance this crossover has to the introduction of Gotham and Batwoman. It's a good way to get fans excited about a new show, after all the very first crossover between Arrow and The Flash served as a backdoor pilot for the latter, and that seems to have worked out pretty well.

More: What Elseworlds Means For the Arrowverse & Batwoman

Elseworlds begins with The Flash on Sunday, December 9, then Arrow on Monday, December 10, and ends with Supergirl on Tuesday, December 11. All episodes air at 8pm.

Source: The CW