Even before Supergirl - co-created by Arrowverse architect Greg Berlanti - debuted on CBS in the fall of 2015, fans speculated about whether Kara Danvers (Melissa Benoist) would meet The CW's lineup of DC Comics superheroes. Last year, Supergirl was confirmed to be part of a multiverse in which The Flash, Arrow, and Legends of Tomorrow exist on Earth-1, while Kara's world was later established as Earth-38. Since then, Kara has not only teamed up with The Flash's Barry Allen (Grant Gustin), but a whole host of Arrowverse heroes this past fall for the 'Invasion!' mega-crossover.

But, Barry and Kara are set to meet once again this season for The Flash and Supergirl musical crossover episode. It will kick off at the end of Supergirl's March 20th episode, 'Star-Crossed', and continue in The Flash's March 21st episode, 'Duet'. Now, the first promo for 'Duet' debuted during tonight's episode of Supergirl.

The CW unveiled the first teaser for 'Duet' [above], which features two moments from The Flash and Supergirl's previous crossover that showcase their team-up chemistry. Then, the promo transitions into a few brief glimpses of the alternate reality in which Kara and Barry will find themselves trapped after being whammied by the Music Meister, played by guest star Darren Criss (Glee).

The Flash Supergirl Music Meister

The recently released synopsis for The Flash's 'Duet' explained the setup fans will see when the musical crossover airs in two weeks. After being whammied by Music Meister, both Barry and Kara will be comatose, trapped in "an alternate reality where life is like a musical" from which they'll need to sing and dance their way out. Based on the vintage sepia tones, clothing, and settings of the scenes from the 'Duet' promo, these glimpses are undoubtedly from that alternate reality - which additionally explains those 1940s set photos for The Flash.

That said, the promo focuses almost exclusively on Barry and Kara. While they'll no doubt be the focus of the episode - and have even been confirmed to sing a duet in the original song "Superfriends" written by Rachel Bloom, creator/star of Crazy Ex-Girlfriend - other Arrowverse characters are reported to have singing parts as well. Joe West (Jesse L. Martin), Cisco Ramon aka Vibe (Carlos Valdes), Winn Schott (Jeremy Jordan), Professor Martin Stein (Victor Garber), and Malcolm Merlyn (John Barrowman) will all have singing roles and will, presumably, appear in the alternate reality.

Still, we know based on set photos of Music Meister that Barry and Kara's friends will have their hands full back on Earth-1 with the musical villain himself. Plus, in addition to Supergirl's Girl of Steel and Winn, Mon-El (Chris Wood) and J'onn J'onzz aka Martian Manhunter (David Harewood) will appear in 'Duet', though they will not be singing. So, with plenty to look forward to in 'Duet', The CW has begun to whet fans' appetites with this first promo - but we'll likely see more footage and photos once the episode's debut is closer.

Next: Iris Plays ‘Key Role’ in Musical Crossover

Supergirl continues Monday, March 20 with ‘Star-Crossed’ at 8pm on The CW.  The Flash Tuesday March 7 with ‘The Wrath of Savitar’ at 8pm on The CW.

Source: The CW