The show flew Santonastasso, a New Jersey teen famous for his zombie pranks, to Tokyo for the stunt.
Andrew Lincoln, who plays Rick Grimes, and Greg Nicotero, the show's special effects master, prepped the 17-year-old fan, who was born with one arm and no legs due to a rare condition called Hanhart syndrome.
The stage was set with Santonastasso in perfect zombie makeup hiding under a craft services trolley, when he pops out and scurries across the floor to scare Reedus, who responds with expletives before reaching out to hug the teen, whom he recognized.
"I've already heard about you. I've already blasted you out to the planet," says Reedus. "Good job, you jerk!"