Tom Cruise Uses His Own Real Ass for Movies, Says 'Mummy' Co-Star Annabelle Wallis

Tom Cruise is a real-life action hero on the set of his movies -- but his ass is even realer ... according to one of his co-stars.

We got Annabelle Wallis -- who starred alongside Tom in "The Mummy" this summer -- and she confirmed 2 stories about him all in a matter of seconds.

She says it's true that Tom saved her life while filming 'Mummy' when something got wrapped around her neck during a stunt. More recently, though, folks speculated he used a prosthetic booty in his 2009 Nazi movie, "Valkyrie" ... and you can kinda see why.