'Flash/Supergirl' musical crossover release date rumors: Showrunner promises original music

The CW's "The Flash" and "Supergirl" are planning to have a musical crossover episode next spring and executive producer Greg Berlanti takes time to talk about his plans for the episode. Before it hits the screen, however, another crossover will happen later in the year. This time it will be one among TV shows "Arrow," "The Flash," and "Legends of Tomorrow."

In an interview with Indiewire, Berlanti talks about the possible choices of music for the episode they're planning. He says, "I have a few ideas for tone and style in my head but we're just starting to talk about what that can be. I do want to try and get an original piece of music written."

There are rumors going around that Joss Whedon, director of "The Avengers," will be directing the musical episode. He previously directed the musical episode for "Buffy the Vampire Slayer."

Fans also shouldn't worry if the two leads will have any trouble singing. Grant Gustin (Barry Allen/The Flash) and Melissa Benoist (Kara Zor-El/Supergirl) have already showcased their vocal chops when they appeared in the musical hit show "Glee." Gustin performed a cover of "Smooth Criminal" by Michael Jackson while Benoist joined an ensemble performance of "Wannabe" by the Spice Girls.

Berlanti also talks about the crossover feature that is happening later this year. The story will span for three hours and it will be told through three consecutive episodes of "The Flash," "Arrow," and "Legends of Tomorrow." Though the story has nothing to do with the "Supergirl" series, Kara will still appear in the crossover.

Berlanti says, "We're telling one cohesive story; Supergirl will participate, but the storyline doesn't actively begin there... Just today I was holding the three scripts back-to-back – that's 180 pages of material."

With actors participating in three separate productions, he also says that a lot of the trouble comes with trying to figure out all of the actors' schedules and making sure none of them have any conflicts with filming.

The crossover episode is said to come by the end of November and the musical episode is expected to air next year.