It's confirmed and it's going to happen. Michael Keaton who had once played the role of Bruce Wayne in Tim Burton's Batman films will be returning in his black suit again as Batman in the next Flash movie, starring Ezra Miller. 

Director Andy Muschietti had stated in August that he had big plans with a substantial role for Keaton even though Ben Affleck was also set to play the role of The Dark Knight after appearing as Batman in Batman Vs Superman, Suicide Squad, and Justice League. Entertainment Weekly has reported that Spider-Man: Homecoming actor will also be a part of the project. 

Michael Keaton Ezra Miller

The movie, The Flash has taken inspiration from the original animated film, The Flashpoint Paradox from DC Comics where Barry Allen runs at lightning speed. The run teleports him to a parallel universe where Superman is a powerless figure, Bruce Wayne is dead, Bruce Wayne's father, Thomas Wayne becomes Batman after the death of his son. His wife, Martha Wayne turns into the Joker out of the madness of watching her son die from the bullet that was meant to hit her. 

Barry Allen runs to a world where his mother is still alive, but in order to rescue his mother, the bullet with which Wayne was attacked in the dark lanes of Gotham, shifted position and hit Bruce Wayne instead. The animated film had been one of the most remarkable works of the DC Comics animated franchise. 

Perhaps, Michael Keaton will be seen in the role of Thomas Wayne turned Batman, while in the other paradigm, Ben Affleck will remain the Batman. 

Muschietti, who previously directed It and Chapter Two for Warner Bros., announced on Instagram that The Flash is starting production. The role will be reprised by Ezra Miller, who previously played the superhero character in Justice League

The Flash has also roped in Young and the Restless Daytime Emmy nominee Sasha Calle as Supergirl, making the actress the first Latina to portray the character.