The 33-year-old British actor hid his identity under a Guy Fawkes mask (as worn by the eponymous anti-hero in V for Vendetta), and posed for a photo with Smith, who had no idea he was anyone but a normal fan.
"Best Comic Con yet. I got to be here for Justice League but couldn't miss Suicide Squad," Cavill captioned the hilarious clip.
The first trailer for Cavill's upcoming Justice League team up (which doesn't actually feature any footage of the handsome star) debuted at SDCC on Saturday. Smith's Suicide Squad, which also stars Jared Leto, Margot Robbie, Jai Courtney and Cara Delevingne premieres Aug. 5.