Robert Downey Jr. is in final negotiations to join Marvel’s “Captain America 3” as billionaire and superhero Tony Stark, an individual with knowledge of the situation told TheWrap.

The third “Captain America” is set to start production in early 2015 for a May 2016 release. Downey has already committed to play Iron Man once again for the upcoming “The Avengers: Age of Ultron” and “The Avengers 3.”

Also read: Robert Downey Jr. Hints That Someone Else May Wear the Armor for Fourth ‘Iron Man’ Movie (Video)

The popularity for the “Captain America” franchise has grown over the first two films, “Captain America: The Winter Soldier” brought in twice as much as “The First Avenger,” which made $371 million in 2011.

As TheWrap previously reported, Downey hinted in a recent appearance on “Ellen” that he was in negotiations with Marvel on something, but he was dodgy on the details.

“I know there’s going to be more Marvel movies, and they have big ideas of how to do it best,” Downey told Ellen DeGeneres. “We’re in the middle of negotiations, blah blah blah.”

Then later, he was equally secretive with David Letterman.

Also read: Robert Downey Jr. Confirms ‘Iron Man 4’ in the Works (Video)

“There is no script for ‘Iron Man 4,’ but they do have a plan and I think they’re going to announce it,” Downey said on the “Late Show.” He added, “You know, they’re very secretive, Marvel.”

When Letterman pressed, he dished, “Just between us, no. But I’m gonna do other stuff with Marvel. I’m still gonna be involved with Marvel and there’s gonna be plenty of fun stuff to happen.”

There’s still no official word if the actor will return for a fourth installment of “Iron Man,” but it sounds like Marvel will keep him busy in the meantime.

Representatives for Robert Downey Jr. and Marvel have not returned TheWrap’s request for comment.

Variety was first to report the news.