VIDEO: First Look - Melissa Benoist, Grant Gustin Perform 'Super Friends' on Musical Episode

Below, check out a first look at Grant Gustin and Melissa Benoist performing the original song "Super Friends," on the 'Duet' musical crossover episode of THE FLASH and SUPERGIRL. The song was penned by CRAZY EX-GIRLFRIEND creator and star Rachel Bloom. The episode airs tomorrow, March 21st on The CW.

The Flash/Supergirl musical episode is described as follows: "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."