“Supergirl”-”The Flash” Musical Crossover Spoilers: Grant Gustin Says Episode Is “Literally A “Glee” Episode: Will We Expect Some Show Alums?

A couple of weeks before the highly-anticipated musical crossover episode of The CW superhero shows “Supergirl” and “The Flash” debuts on the small screen, star Grant Gustin joked how the episode would might as well be another “Glee” episode, Entertainment Weekly reports.

Darren Criss, who will be playing the DC Comics villain Music Meister, agrees, and even made comparisons with working with Gustin both in the Ryan Murphy musical comedy-drama and The CW crossover episode, which is aptly titled “Duet.”

“It is funny that the last time I worked with Grant, he was the bad guy and he was singing at me, and now I’m the bad guy singing at him,” Criss said, referring to his character Blaine Anderson receiving a slushie facial from Grant’s Sebastian Smythe back in 2012.

Aside from the coincidental casting, there will be no other "Glee" guests however. But the episode promises more musical numbers similar to a typical "Glee" episode.

In “Duet,” the episode will have Gustin, Barry Allen/The Flash, and Melissa Benoist (Kara Danvers/Supergirl) trapped by the Music Meister (Criss) in a dream sequence, Comicbook.com reported.

And just like “Glee,” Den of Geek said expect a lot of musical performances. Benoist will sing a cover of “Moon River,” Gustin will sing “Runnin' Home To You” - an original by Benj Pasek and Justin Paul, the two will join forces for original song “Super Friend” by “Crazy Ex-Girlfriend” creator and star Rachel Bloom, and Jeremy Jordan, Carlos Valdes and John Barrowman will do a cover and dance to “Put A Little Love In Your Heart.”

“Duet” will kick off with the end-of-the-episode scene of “Supergirl”’s March 20 episode to “The Flash”’s March 21 episode.