After years of development, actor Dwayne Johnson says he will start filming "Black Adam" in 2020, adding he is elated that his superhero dream is turning into a reality.

Black Adam is Shazam's arch-nemesis and a complex anti-hero with a rich history of his own.

The film based on the DC villain will open on December 22, 2021, days after "Avatar 2" releases on December 17. Johnson announced the film's release date on Thursday, reports hollywoodreporter.

"Like most kids growing up, I dreamed about being a superhero. Having cool superpowers, fighting for what's right and always protecting the people. It all changed for me, when I was 10 years old and was first introduced to the greatest superhero of all time - 'Superman'. As a kid, Superman was the hero I always wanted to be. But, a few years into my fantasy, I realised that Superman was the hero, I could never be," Johnson wrote on Instagram.

He continued: "I was too rebellious. Too rambunctious. Too resistant to convention and authority. Despite my troubles, I was still a good kid with a good heart -- I just liked to do things my way. Now, years later as a man, with the same DNA I had as a kid -- my superhero dreams have come true. I'm honoured to join the iconic #DCUniverse and it's a true pleasure to become, 'Black Adam'. 'Black Adam' is blessed by magic with the powers equal to Superman, but the difference is he doesn't toe the mark or walk the line a This role is unlike any other I've ever played in my career and I'm grateful to the bone we'll all go on this journey together."

The New Line film will reunite Johnson with his "Jungle Cruise" director Jaume Collet-Serra and is a spinoff of Warner Bros. and New Line's "Shazam!", Zachary Levi's superhero film that opened in April.

"Black Adam" was at one point scheduled to have been in a main "Shazam!" movie but the studio and producers ultimately decided he warranted his own movie. Johnson has been attached to play Black Adam for more than a decade.

Although Black Adam has traditionally been a villain, Johnson is selling him as a hero.

"He's a rebellious, one of a kind superhero, who'll always do what's right for the people," Johnson wrote on Instagram, adding: "But he does it his way. Truth and justice - the BLACK ADAM way."

Black Adam debuted in 1945's "The Marvel Family No. 1a as an earlier version of Shazam who was corrupted by the power. That was a role he maintained through his eventual reappearance in the late 1990s comic book series "The Power of Shazam!", which narrated his backstory, revealing that he had actually been corrupted by an external force.