'The Flash' season 3 spoilers: Musical crossover with 'Supergirl' names Glee star as Music Meister baddie

"The Flash" and "Supergirl" air Tuesdays on The CW

Melissa Benoist and Grant Gustin present at the 73rd Golden Globe Awards in Beverly Hills, California, January 10, 2016. Reuters/Paul Drinkwater/NBC Universal/Handout

Before they were superheroes, viewers might remember Grant Gustin and Melissa Benoist singing and dancing to some tunes on “Glee.” Now that their current shows are about to air a musical crossover, it is not much of a surprise that The CW has enlisted the services of a fellow “Glee” alumnus, who even happens to be one of the most closely followed actors in the show.

Spoiler alert! This article contains “The Flash” spoilers. Read on if you would like to know what happens next before the next episode airs.

Just when fans might have thought that former “Glee” stars turned DC icons could not get more exciting, it looks like they are in for more elements from “Glee.” It has been confirmed that actor Darren Criss, who has starred with Melissa Benoist and Grant Gustin in “Glee,” will be joining them once again in the two-part musical crossover between “The Flash” and “Supergirl.”

Criss will be joining in as the Big Bad Music Meister, which is really a villain in the DC Universe, writes TV Line. Executive Producer Andrew Kreisberg reveals that considering that both their Flash and Supergirl are alumni of “Glee,” their best option was to make them go up against another fan favourite. This happens to be Darren Criss. He adds that Criss has blown him away by his talent over the years and they are very excited to see what he has to bring in his own take of Music Meister.

As for which characters will be seen singing, it has already been officially confirmed that Broadway veterans Jesse L. Martin, John Barrowman, Victor Garber, Carlos Valdes and Jeremy Jordan will be lending their voices. All that music, coupled with the action that “The Flash” and “Supergirl” had been able to offer, will be a wondrous sight to be seen very soon.

This anticipated crossover will air on Monday March 20 and Tuesday March 21 at 8|7. The crossover will start at when “Supergirl” ends, just so most of the music in “The Flash” will be seen.

“The Flash” airs every Tuesday at 8 p.m. on The CW. It also airs on FOX8 in Australia.

Melissa Benoist Confirms Glee Reunion for Supergirl and The Flash Musical Crossover