David Harbour shared spoilers about his Black Widow character with his Stranger Things bosses to ensure they didn't come up with similar storylines.
Since his TV character Sheriff Hopper was in Russia at the end of the third season of Stranger Things, the actor wanted to make sure his Russian Black Widow character, Alexei Shostakov, would be significantly different.
Harbour knew he was taking a chance in spilling top-secret details from the Marvel movie, but he also felt certain he had to tip off Stranger Things co-creators Matt and Ross Duffer.
"The circle of secrets contains other people that keep secrets," he told E! News. "I felt like I could share Marvel secrets with them because, you know, they understand how to desperately keep a secret and the power of that."
He also sent the Duffers production and costume photos to make sure the two characters would be nothing like each other.
"Both things also take place, at one point, in a Russian prison.
"One of my biggest concerns though is that I want to make them different," Harbour said. "The most obvious parallel is that they're both father figures in a sense, and in a weird way, they're both father figures to adopted daughters."
Elsewhere, the star noted that his Black Widow character is louder and hairier than the hot-tempered small-town sheriff he plays on TV.
"Alexei's narcissism, even his loudness of personality, even the amount of hair he has on his body is, like, all of it is trying to make this character behave much differently based on these set of circumstances, based on these traumas," he added.
However, Harbour refused to spill any further details on the highly anticipated action film or the Netflix series.