The actor was warned that Serena is a big fan of his "Doctor Strange" character just before fashion's big night but he still wasn't prepared for their first meeting at the bash.
"She's a massive, massive Marvel fan," he tells "Good Morning America", revealing she blamed him for the end of the "Avengers" films.
"She's like, 'You don't understand, you are ruining my life', and I'm like, 'Sorry, we just met...!' She was like, "I'm just a stupid fan, I'm too involved... It just matters too much to me!'."
She also told Cumberbatch that she had been putting off seeing the final "Avengers" movie, "Avengers: Endgame": "She said, 'I've been in a funk all week, because I think I know what's gonna happen'. I said, 'Have you seen it yet?' and she said, 'No!'
"I said, 'Go and see it, get through it. It's an amazing film'."