Ezra Miller improvised many of his scenes in 'Justice League'.

The 25-year-old actor stars as Barry Allen aka The Flash in the new DC Extended Universe movie and he was encouraged to react to his co-stars and come up with many of his own lines and movements as the comic of the superhero squad.

Speaking at the world premiere of 'Justice League' at the Dolby Theatre in Hollywood on Monday (13.11.17), Miller said: ''There was a lot of improv. I improvised every day, on every scene. It was just a good way to work with this character and thankfully I was allowed to do it. I consulted with the woman who taught me improv and I got to sort of delve back in to that. My own acting training was in improv. It was so much fun. When you have other layers and characters you can bounce off, it was really great.''

'Justice League' focuses on Ben Affleck as Batman, Gal Gadot as Wonder Woman, Miller as The Flash, Jason Momoa as Aquaman and Ray Fisher as Cyborg, who must come together to protect Earth from the alien threat of Steppenwolf.

Miller also revealed he loves how the meta humans in the blockbuster ''break the rules'' to save the world.

He said: ''I think it's the idea that they break the rules. Superheroes break the rules of physics and puts it to a good purpose. They have to break the rules to save the world.''