With 2016's "Invasion" weeklong event out of the way, the CW's "Flash" and "Supergirl" series now have another big crossover on the horizon. When the two shows meet later this season, they'll be singing and dancing -- because the crossover is a musical crossover. The event will feature Darren Criss as the villain Music Meister, and it turns out it will shine a spotlight on one "Flash" player in particular.

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TV Line talked to co-showrunner Aaron Helbing about the episode, who revealed that Iris West (Candice Patton) will have a big part to play in the adventure.

“She plays a pretty key role in the musical episode. The story really centers around Iris,” said Helbing. “Aside from Barry and Kara, Iris plays a huge role in the musical.” The episode will also feature songs from "Crazy Ex-Girlfriend's" Rachel Bloom and the “La La Land” songwriting duo of Benj Pasek and Justin Paul.

“The Flash” and “Supergirl” musical crossover will start with a lead-in scene on the March 20 episode of “Supergirl,” and continue in full on the March 21 episode of “The Flash.” The episode will include musical numbers from “The Flash” stars Grant Gustin, Jesse L. Martin and Carlos Valdes; “Supergirl” stars Melissa Benoist and Jeremy Jordan; and “Legends of Tomorrow” co-star Victor Garber and “Arrow” regular John Barrowman; along with “Glee” alum Darren Criss as the Music Meister, the episode’s antagonist.

Starring Grant Gustin as the Scarlet Speedster, "The Flash" airs Tuesdays at 8 pm ET/PT on The CW. The series also stars Jesse L. Martin, Tom Cavanagh, Carlos Valdes, Candice Patton, Danielle Panabaker, Keiynan Lonsdale and more.