When Warner Bros.' The Flash speeds into theaters in "Justice League Part One," he won't be played by Grant Gustin, who has appeared in the role on The CW's hit television show "The Flash." During an interview with Daily News, director Zack Snyder -- who oversees the development of the expanded DC Cinematic Universe -- explained why Ezra Miller, and not Gustin, landed the role of the Scarlet Speedster.

RELATED: The Flash Is Heading To "Supergirl," But How Will "Supergirl" Tie Into "The Flash"?

"I'm very strict with this universe and I just don't see a version where...that [tone is] not our world," Snyder explained.

"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," he added.

Boasting films like "Man of Steel" and "Batman v Superman," Snyder's DC Cinematic Universe is known for its darker trappings, where Gustin's "The Flash" is often lighthearted and humorous. This is likely what Snyder is referring to when it comes to the difference in tone between the two worlds.

"Batman v Superman: Dawn of Justice," the next installment of the DC Cinematic Universe, opens on March 25, 2016. "Justice League Part One" opens on November 17, 2017. "The Flash" opens on March 16, 2018. "Aquaman" opens on July 27 2018.