LOS ANGELES, June 13 (Reuters) - “The Flash" debuts in movie theaters on Friday after a series of delays and personal setbacks by star Ezra Miller, a key part of Warner Bros’ battle for the summer box office that also starts the reboot of the DC Extended Universe franchise under its new co-chairman James Gunn.

Miller portrays Barry Allen who, as a superhero, the Flash, uses his superspeed to travel back through time to try to prevent his mother’s death. Miller plays both The Flash and his younger self throughout the film.

The Flash gets stuck in the past with Supergirl portrayed by Sasha Calle and Batman played by the original cinematic Batman, Michael Keaton.

The film's premiere was pushed back by the COVID-19 pandemic and by Miller's mental health struggles and arrests in 2022, including second-degree assault and burglary.

Miller, who identifies as non-binary and uses they/them pronouns, did not speak to the press to promote the film but did make their first public appearance in almost two years at Monday's premiere with fellow cast members.

"Really it's a beautiful moment for me," Miller told Warner Bros at the premiere. "It's really wonderful to see everybody and have a moment to celebrate this movie, that, as you say, has been sort of a journey."

Ben Affleck, who portrays Batman in some scenes, told Warner Bros it was "nice" to play a wiser character with something to impart to younger characters.

Calle, the only actor from the film to speak with Reuters, said little about Miller's role.

When asked how audiences should approach the movie after Miller’s controversies, she said the “beautiful" film was made with thousands of people who put their hearts into it.

The speedster story is garnering mixed reviews, currently rated 72% on the review aggregator Rotten Tomatoes.

"Much of the advance publicity has focused on Ezra Miller's string of controversies and legal issues," David Rooney of the Hollywood Reporter said. "But the troubled star turns out to be the film’s chief asset, bringing humor, heart, and a vulnerability not often seen in big-screen superheroes."

An estimate from a person familiar with the release predicts "The Flash" will earn $70-75 million in its opening weekend, less than recent standouts this year. "Spider-Man: Across the Spider-Verse" brought in $120.5 million in its opening weekend, second to the $146 million earned by "The Super Mario Bros."