Affleck recently shared a set video featuring Deathstroke in action (watch below).
DC Entertainment president, chief creative officer and the co-chief of DC movies, Geoff Johns, confirmed Joe Manganiello as Deathstroke for the Batman movie.
In addition, Joe Manganiello took to Twitter to confirm Deathstroke by reteweeting Ben Affleck's video and adding, "It's on..."
WSJ notes Geoff Johns wouldn't confirm Deathstroke for the Justice League film, and also wouldn't say when the solo Ben Affleck Batman movie is going to be released, though it does appear the footage did reveal Deathstroke in Justice League.
Both Geoff Johns and Ben Affleck are writing the Batman movie script, with Affleck directing.
Joe Manganiello is known for True Blood, Magic Mike, as well as playing the bullly Flash Thompson in the Sam Raimi Spider-Man movies.
Deathstroke was most recently played by Manu Bennett on Arrow, which is not connected to the movies. Stephen Amell recently said he still thinks Deathstroke could return to the Arrow TV universe with Deathstroke appearing in the movies at the same time.
Justice League has a November 17, 2017 release.