“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)

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Mariah kills Cottonmouth, "Luke Cage"
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The death of Black Canary, "Arrow"
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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
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The CW
A new brand of vigilante arrives, "Sweet/Vicious"
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The return of Joker? ("Gotham")
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