The film's extra let it spill that Malone would play the masked superhero who first appeared in Frank Miller's comic book 'The Dark Knight Returns', reported Ace Showbiz.
The unnamed extra could be facing a hefty USD 5 million fine for spoiling the movie's top secret after signing a non-disclosure agreement with Warner Bros.
Malone was not seen on the set, but her latest appearance supported the theory. Her Instagram photo sees her sporting short red hair identical of the comic book character.