The police officer appeared to lose his life at the end of the show's season three, and Harbour reveals he still has no idea if his character survived.
During an appearance on U.S. show "Late Night With Seth Meyers" on Monday, October 7, the actor said, "I always knew that Hopper had to make a sacrifice. He's a jerk and he needs to pay for that in some way, so, I thought he'd make the sacrifice and then the script came out and... at the end, (in) the post-credits scene there's 'the American', and I'm like, 'Oh, clearly I'm the American...!' And then, I haven't gotten many phone calls."
He then agreed to FaceTime the Duffer Brothers, who created the hit show, and ask them what their plans were.
"I have a question...," he said. "Am I dead? Is Hopper dead?".
"I mean, we're still figuring it out, David," Ross Duffer responded.
Harbour shot back, "You guys are a lot of help, thanks. Really wonderful work. Good luck with season four. Love you guys, love you, bye".