The 39-year-old actor will play Deathstroke -- a villainous mercenary who gains superpowers in a clandestine military experiment -- in the upcoming DC Comics franchise film, the Wall Street Journal reports.
In August, Affleck, who will also direct the flick, teased who Batman's adversary would be in a Twitter video introducing Deathstroke (but not who plays him!).
While we can't wait to see Affleck v. Manganiello, the untitled Batman stand-alone does not yet have a release date, while DC's Justice League is set to hit theaters in November 2017. It's unclear whether Deathstroke will have a cameo in that film.
Watch the video below to see Affleck explain why he makes the perfect "older" Batman.