Jamie Campbell Bower’s incredible transformation into “Stranger Things” season 4’s villain was a huge shock to co-star Millie Bobby Brown.

In an interview with Variety, Bower opens up about the work that went into the full-body makeup and prosthetics that turned him into the grotesque Vecna.

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As it turns out, the makeup was so frightening it actually made Brown cry when she first saw it.

“They brought her up into a position where she’s bound. I walked up to her [as Vecna] and she burst into tears,” Bower says. “She wouldn’t look at me and she was visibly just disgusted by the whole thing.”

He adds, “After she cried and I made it obvious that she knew it was me, one of the things she said was that, ‘I knew it was you when I could smell cigarettes,’ because I’m a smoker.”

In “Stranger Things 4”, Brown’s Eleven learns that she was responsible for sending Venca into the Upside Down, creating the monster he has become.

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To create that monster, the Duffer Brothers hired acclaimed prosthetics designer Barrie Gower, known for his work on “Game of Thrones” and “Harry Potter and the Deathly Hallows: Part 2”.

Bower required 25 pieces of latex and silicone glued to his body, with only some additional CGI added later to sell the effect.

The application of the prosthetics and makeup took over seven hours each day, with another hour to remove it all once shooting wrapped.