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Marvel announced his role during its San Diego Comic-Con panel.
Stoll was cast in the movie back in March, but until now his role has been unknown. He will play Darren Cross who becomes Yellowjacket in the comics.
Corey Stoll plays Darren Cross, aka Yellowjacket in #AntMan. He was Hank Pym's mentee before things got sour. #MarvelSDCC
- Ryan Penagos (@AgentM) July 27, 2014
During the panel, Evangeline Lilly ("The Hobbit" trilogy, "Lost") was also confirmed to play a lead role.
The two join Michael Douglas and Paul Rudd in the movie.
Footage from the film was screened during the panel.
"Ant-Man" will begin filming August 18 and will be in theaters July 17, 2015.