Watch Grant Gustin, Melissa Benoist in First 'The Flash'-'Supergirl' Musical Crossover Teaser (Video)

“The Flash” and “Supergirl” are crossing over again, but this time under very different circumstances, as witnessed in the first teaser for the highly-anticipated musical crossover episode released Monday night.

Grant Gustin and Melissa Benoist are seen in 1940s garb, potentially tangling with mobsters, and yes, getting their musical on, especially Benoist, whose Supergirl is seen behind a microphone on a stage.

While the vast majority of the action will take place on “The Flash” in an episode fitting entitled “Duet,” the story will be set up at the end of the “Supergirl” episode preceding it the day before — much like with this year’s four-show crossover.

Also Read: 'Supergirl' Adds 'Hercules' Star Kevin Sorbo as New Villain

“Supergirl” will air Monday, March 20, followed by “The Flash” on Tuesday, March 21.

“Duet” will be directed by Dermott Downs and will feature singing performances from Arrowverse actors Gustin (Barry Allen/The Flash), Benoist (Kara Zor-El/Supergirl), Jesse L. Martin (Joe West), Victor Garber (Martin Stein/Firestorm), Carlos Valdes (Cisco Ramon/Vibe), Jeremy Jordan (Winn Schott), and John Barrowman (Malcolm Meryln), while also including non-singing guest star appearances from David Harewood (Hank Henshaw/Martian Manhunter) and Chris Wood (Mon-El).

Also Read: 'Supergirl' Casts Former Lois Lane Teri Hatcher in Recurring Role

Both “The Flash” and “Supergirl” were recently renewed for new seasons by The CW for Seasons 4 and 3, respectively.

“Supergirl” airs Mondays at 8 p.m. ET on The CW and “The Flash” airs Tuesdays at 8 p.m.

10 Most Epic TV Superhero Moments in 2016, From 'Arrow' to 'Luke Cage' (Photos)

Heartbreaking deaths, noble sacrifices, network moves and crossover events, superheroes sure have had a roller coaster of a year.
"Supergirl" flies to The CW
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The CW
Mariah kills Cottonmouth, "Luke Cage"
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The death of Black Canary, "Arrow"
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Staircase fight, "Daredevil"
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Netflix
When Barry met Kara, "Supergirl"
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CBS
"Agent Carter" canceled
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Lincoln's sacrifice, "Agents of SHIELD"
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Legends of SuperFlarrow
More than a dozen DC comic book characters appeared on screen together when The CW tackled its most ambitious crossover yet, bringing together the heroes of "Arrow," "The Flash," "Supergirl" and "Legends of Tomorrow."
The CW
A new brand of vigilante arrives, "Sweet/Vicious"
Forget superpowered comic book characters, the newest heroes on the street are all about taking down campus rapists, making Jules and Ophelia the superhero team the world needs right now.
MTV
The return of Joker? ("Gotham")
He was killed off on the show in 2015, but Cameron Monaghan seemed to hint his Joker wasn't done terrorizing the city in a tweeted-and-deleted photo.
Fox