(CNN) - Spoiler alert: "Avengers: Endgame" is not the first movie in which Mark Ruffalo and Brie Larson both appear.
And if you didn't know, it's all good because apparently Ruffalo didn't either.
"Entertainment Tonight" surprised the actor on the red carpet for the premiere of the new Marvel movie by sharing with him that his co-star had appeared in one of his most beloved films, "13 Going on 30," which debuted in 2004.
"She was a mean girl," Ruffalo said upon seeing a photo of Larson in character from the movie. "Oh my God. I didn't know that."
Larson reprises her role from her stand-alone movie as Carol Danvers/Captain Marvel in "Avengers: Endgame" and Ruffalo is back as Bruce Banner/Hulk.
The now-29-year-old actress was pretty young when she was in the movie and Ruffalo, 51, explained why he didn't know they were in the same hit film.
"We didn't work together," he said.
"13 Going on 30" starred Jennifer Garner as a young girl who wakes up as an adult and reconnects with her now also adult childhood friend, played by Ruffalo.
"Avengers: Endgame" hits theaters Friday.