Sorry in advance, because we’re probably about to throw a wrench into your “Stranger Things 4” theories with this reveal.

David Harbour told TheWrap in a recent interview that he initially believed his character Jim Hopper — who sacrificed himself at the end of Season 3 to save Joyce (Winona Ryder), their children, basically everyone in Hawkins, Indiana, and possibly even the entire world — is “The American,” a character referenced, but not shown on screen, during the finale’s post-credits scene.

But seeing as creators Matt and Ross Duffer, a.k.a. The Duffer Brothers, have yet to give him any details about Season 4, Harbour told us he’s grown less sure about the possibility that Hopper is, in fact, still alive and “The American,” who is being held captive inside a facility in Russia, along with the Demogorgon.

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“So [The Duffers] told me the arc of the season, and then I think we got Episode 8 like a couple months before we shot it,” Harbour, who recently received a Screen Actors Guild Award nomination for Outstanding Performance by a Male Actor in a Drama Series, told TheWrap. “And I remember reading that episode, and they hadn’t told me this whole thing about this Russian facility at the end and how that was gonna be the sort of teaser and like ‘The American’ and the Demogorgon. They hadn’t told me about any of that, actually, and I just read it in the script and I thought it was amazing.”

“And I really thought I was ‘The American,’ and then I haven’t heard a lot from them (laughs),” Harbour said. “So I really don’t know if I am. But I thought I was, but it was never discussed.”

He added: “I didn’t ask [The Duffers], ’cause I felt confident I was — and now I’m not so confident.”

While Harbour says he doesn’t “know what’s happening” with the upcoming fourth season — which has not been given a premiere date by Netflix — he is keeping his schedule open just in case Hopper is “The American.”

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“I’ll tell you this, I don’t have work lined up right now. I am working on a book, so I’m sort of focused on that right now and I don’t really have acting worked lined up. So theoretically, if somebody called me, I could probably get on a plane and do something,” he said.

And yes, Harbour definitely wants to return.

“My hope is the same as yours,” he said. “My hope is that there is some sort of resurrection [for Hopper], but I don’t know. I know they haven’t gone into production yet.”

Hopper’s death came in the final episode of the season, when a clearly heartbroken Joyce (Winona Ryder) had to pull the key to close the gate to the Upside Down, vaporizing Hopper — who was in close proximity to the blast — in the process, as she looked on in horror from behind protective glass. And this was just after the two had finally gotten together romantically.

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“For her, and me as well, we just sort of didn’t want to see each other on that day,” Harbour told us. “It was very late in the season, it was the last thing I shot. And so it was just me looking up at a window. And for me, in that moment, it was sort of very easy. I mean, I did some work on what I wanted to convey. But it was like the culmination of this three year journey with this actress that I adore, and I adore working with, and I’ve never experienced anything like the co-star working relationship I have with her. And so it was kind of the culmination of that. So in that way, it was easy to just have that be informed by what I have felt over these last three years as opposed to anything we could do in the moment.”

“I think that it was just about letting go,” he continued. “It’s always hard for Winona at the end of a season. I think she, like me, we get very attached to a season and then it’s like saying goodbye. And this was a big one. And we didn’t have each other there, we just sort of stared off. I thought it was so beautiful when I watched it put together. I mean, it’s such a gracious moment of Hopper to nod and sort of smile and I love that about him in that moment. I love that he let go that way, that he lets her off the hook for something that she has to do for their kids. I mean, their kids are more important than them, clearly, in that moment. I love that moment.”

Readers can watch Netflix’s featurette of Harbour discussing his performance in Season 3, which is exclusive to TheWrap, via the video above.