"Supergirl" and "The Flash" to do a musical crossover episode

Grant Gustin as The Flash on "The Flash."

Jack Rowand/The CW

"Supergirl" and "The Flash" stars Melissa Benoist and Grant Gustin will soon get to revisit their "Glee" roots.

The two stars -- who got their start on Ryan Murphy's now-defunct tuneful high school soap -- will be singing once again on an upcoming musical crossover episode featuring their CW superhero characters, executive producer Greg Berlanti announced during a Television Critics Association panel Thursday.

"Yes, there will be a musical crossover," Berlanti told reporters. "There's going to be a musical pair of episodes in the back half of the year between Supergirl and Flash."

The superheroes won't be singing original material, though. "I think they're going to be mostly preexisting songs," Berlanti said.

Aside from Benoist and Gustin being former "Glee" cast-members, "Supergirl" sidekick Jeremy Jordan and "The Flash" co-star Jesse L. Martin are both Broadway veterans.

"So many times it's a musical episode off the set, and I think on all the shows, we love to use all of the character talents as much as possible," Berlanti said. "We've toyed with who potentially the villain could kind of be. My sense is we'll be very careful about how it is they kind of break into song and there will probably be an element of being in some character's head at the time."

An unrelated network-wide crossover event between "Supergirl," "The Flash," "Arrow" and "Legends of Tomorrow" is also planned for December -- though with decidedly less singing.