Report: Robert Downey Jr. to join 'Captain America 3'

This could be big news -- Variety reports that Robert Downey Jr. is close to signing a deal to appear in Captain America 3, which would significantly expand Marvel's box-office prowess by bringing  the "Civil War" story line to the big screen.

Downey will reprise his popular Tony Star/Iron Man role for the film, which is targeted for a May 2016 release.

In "Civil War," which was originally a 2006-2007 Marvel miniseries comic-book event, Stark squares off against Steve Rogers/Captain America (Chris Evans) over the Superhero Registration Act, which requires those with superhuman powers to register with -- and work for -- the government.

Downey is already set to play Iron Man in two movies next year -- The Avengers: Age of Ultron and The Avengers 3.
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