Robert Downey Jr. is close to finalizing a deal with Marvel Studios that would see his Tony Stark take on Steve Rogers in the third instalment of Captain America, Variety reports.

The addition of Downey would finalize the missing link in the studio’s “Civil War”; storyline, where Captain America and Iron Man battle it out over the Superhero Registration Act — legislation which forces anyone with superhuman abilities to notify the U.S. government.

Marvel teased the storyline via social media today by tweeting out a poster for the upcoming film. “#CivilWar #1 — Summer 2015,” the promo was captioned.

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The storyline could potentially see Downey’s Iron Man extended over several films.

According to Variety, the deal, which is now in its final stages, initially required a much smaller presence from Downey’s Stark and did not align itself with the actor’s intended plan for the character.

As it stands, and after all is said and done, Downey is said to collect $40 million dollars from his participation in the Captain America 3 alone. And his pay day is set to increase if the film outperforms The Winter Soldier‘s $714 million box office (worldwide) gross.

Filming on the movie is slated to begin in the spring. The Winter Soldier directors Anthony and Joe Russo return to helm the third instalment.