You never know who might be hiding behind the masks at Comic-Con.
Disguised in a giant baboon mask, Leto snapped pictures with a fan dressed as his Joker character from Suicide Squad.
“He had no idea. :),” the actor, 43, captioned.
The Incredible Hulk was also strolling around unnoticed around the convention, disguised as a cigar-smoking, mustached old man.
“Got to hide out and enjoy #comiccon2015,” the Avengers actor, 47, tweeted.
Ruffalo and Leto aren’t the first celebrities to take advantage of identity-concealing costumes at Comic Con. Last year, Daniel Radcliffe had a blast going to the event undercover as Spider-Man.
“It’s great to be able to put on a mask and interact with people who don’t know who I really am,” he told Entertainment Weekly. “I spoke in an American accent the whole time. I felt like a spy about to be found out at any moment.”