The 23-year-old actress is reportedly a martial arts expert and is reinventing herself by training with a top combat solider for her new film, reported Daily Star.
"No-one knows this but Kristen is a martial arts expert, she's practised karate since her fifth birthday. Teen romance roles like 'Twilight' are her past," a source said.
"She has learnt brutal torture skills for her new movie to prove she's a great actress and not just Robert Pattinson's ex-girlfriend," the source added.
Stewart has already developed an impressive six-pack by training with a soldier from the Israeli army who fought in the Lebanese war.