The CW has debuted the first promo for the upcoming musical crossover between "The Flash" and "Supergirl," which is set to air March 20 and 21 on the network. While the clip is short, it features Kara and Barry dressed in dapper, 1940s clothes.

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The promo features a snippet of music that sounds very classic suggesting that most of the music in the crossover will also be '40s-themed. Considering one of the songs is written by the Academy Award-winning songwriting duo from "La La Land," there's a strong chance the episodes will have a truly classic feel.

Take a look at the promo below:

"Supergirl" - "Star-Crossed":

TERI HATCHER (“DESPERATE HOUSEWIVES,” “LOIS & CLARK: THE NEW ADVENTURES OF SUPERMAN”) AND KEVIN SORBO (“HERCULES”) GUEST STAR; DARREN CRISS (“GLEE”) MAKES HIS DEBUT AS THE MUSIC MEISTER – A new villain (guest star Teri Hatcher) comes to National City, putting Supergirl (Melissa Benoist) on high alert. Meanwhile, Winn’s (Jeremy Jordan) girlfriend, Lyra (guest star Tamzin Merchant), gets Winn in trouble with the law. Maggie (Floriana Lima) attempts to help Winn but old loyalties get in the way. The Music Meister (Darren Criss) attacks Supergirl. John Medlen directed the episode written by Katie Rose Rogers & Jess Kardos. Original airdate 3/20/2017.

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"The Flash" - "Duet":

DARREN CRISS (“GLEE”) GUEST STARS AS THE MUSIC MEISTER IN THE FLASH AND SUPERGIRL MUSICAL CROSSOVER – Barry (Grant Gustin) and team are surprised when Mon-El (guest star Chris Wood) and Hank Henshaw (guest star David Harewood) arrive on their Earth carrying a comatose Supergirl (guest star Melissa Benoist) who was whammied by the Music Meister (guest star Darren Criss). Unable to wake her up, they turn to Team Flash to save her. However, the Music Meister surprises The Flash and puts him in a similar coma, one that Team Flash can’t cure. Kara and Barry wake up without their powers in an alternate reality where life is like a musical and the only way to escape is by following the script, complete with singing and dancing, to the end. Dermott Downs directed the episode with story by Greg Berlanti & Andrew Kreisberg and teleplay by Aaron Helbing & Todd Helbing. Original airdate 3/21/2017.

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"The Flash"/"Supergirl" musical crossover will begin on March 20 and conclude on March 21 at 8pm ET on The CW.