Warner Bros. chose to keep its portrayal of DC superheroes separate between the movies and television shows. Director Zack Snyder then tapped Ezra Miller to play The Flash in the DC Extended Universe, making his debut in "The Justice League: Part One," while Grant Gustin resumes the role of Barry Allen on The CW series.

Snyder's reasoning for casting Miller hints at a darker tone for The Flash character in the movies compared to the TV version, created by Greg Berlanti, Geoff Johns and Andrew Kreisberg. He will begin production on "The Justice League" next month.

"I just don't think it was a good fit," Snyder said of squeezing in Gustin. "I'm very strict with the universe and I don't see a version where... that (tone is) not our world."

Warner Bros. has announced 10 films so far that will expand the DC movie-verse beyond 2013's "Man of Steel" and continues into "Batman v. Superman: Dawn of Justice" on March 25. The studio's decision to follow the multi-verse seen in the comic books (the same characters exist in alternate universes) contrasts with the Marvel Cinematic Universe where everything is connected from the feature films to the ABC shows and Netflix original series.

"Even if Grant Gustin is my favorite guy in the world and he's very good, we made a commitment to the multi-verse (idea), so it's just not a thing that's possible," Snyder said.

Following rumors that Gustin disagreed with Miller's casting, the actor posted a letter on Twitter denouncing the speculating and giving a ringing endorsement to Miller. He admitted that he would have loved to play The Flash in a movie, but playing the character has changed his life.

"I fully support Ezra Miller as Barry Allen and the Flash on the feature side of DC," he wrote in January. "I've never met the guy, but I think he is a fantastic and interesting actor."

"Justice League" will bring together Superman (Henry Cavill), Batman (Ben Affleck) and Wonder Woman (Gal Gadot, make her debut in "Batman v. Superman") as well as Jason Momoa's Aquaman, Ray Fisher as Victor Stone and The Flash.

"The Justice League: Part One" will premiere on Nov. 17, 2017.