Details of Mara's role are being kept secret but Gregg will reprise his role as S.H.I.E.L.D. operative Phil Coulsen from the first movie, confirms The Hollywood Reporter.
Filming on Iron Man 2 is currently underway in California, with returning stars Robert Downey Jr and Gwyneth Paltrow joined by Mickey Rourke, Scarlett Johansson, Sam Rockwell and Don Cheadle.
The superhero sequel has been pencilled in for a May 7, 2010 theatrical release.
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