Gustin was cast as the speedy DC Comics character and his alter ego, forensic scientist Barry Allen, for the hit TV adaptation, which launched on America's CW network in 2014.

He has also appeared in crossover episodes of Arrow and Supergirl, but he won't be reprising his role on the big screen as Snyder has opted instead for Ezra Miller to portray the superhero for his Justice League blockbuster.

Now the filmmaker has explained his reasoning for the casting change, suggesting the light-hearted nature of Gustin's portrayal just didn't work for him.

"I just don't think it was a good fit," Snyder told the New York Daily News. "I'm very strict with this universe and I just don't see a version where... that (tone is) not our world."

Production on the Justice League film is due to begin next month (Apr16).

The Perks of Being a Wallflower star Miller will feature alongside Henry Cavill as Superman, Ben Affleck as Batman, and Gal Gadot as Wonder Woman, who all feature in Snyder's hugely-anticipated Man of Steel sequel, Batman v Superman: Dawn of Justice, which opens in movie theatres this week (begs21Mar16).

Meanwhile, The Justice League Part One will also include Jason Momoa as Aquaman, Amber Heard as his onscreen wife, Mera, and Oscar winner J.K. Simmons as Commissioner Gordon.

The movie is set for release next year (17).