Effects wizards have used CGI technology to splice the silver screen stars into a scene with Theron as she prepares to walk in a fashion show at the Hall of Mirrors at Versailles in France.
The advertisement, for Dior's J'Adore perfume, sees Theron change into a gold gown backstage while appearing to mingle with Dietrich, Kelly and Monroe.
The shoot, which was directed by Oscar-winning director Jean-Jacques Annaud, was a dream come true for Theron.
She says, "It was incredibly glamorous and fantastic. I don't think I'll experience something like that again in my lifetime."