Robert Downey Jr. told Ellen last week that he’s in “the middle of negotiations” with Marvel to reprise his fan-favorite role of Tony Stark in future films, and now sources are claiming that the actor is on the verge of signing on to Captain America 3. Tony Stark’s Iron Man and Captain America both play a key role in the Civil War storyline in Marvel’s comic books, and with the company announcing plans to reboot that popular miniseries next year,  many are speculating that that storyline will soon play out on the big screen.

In the comics, Stark and Captain America’s alter-ego Steve Rogers fight over the Superhero Registration Act, which forces all those with superhuman powers to reveal their identities to the U.S. government. Stark supports the program, but Rogers believes it threatens civil liberties and is forced to fight his former Avengers-teammate. The Civil War miniseries launched in 2006, and was the first major crossover of Marvel’s biggest characters.

Marvel announced plans to reboot the miniseries in 2015 at New York Comic Con on Monday, leading people to believe that Robert Downey Jr.’s potential involvement in Captain America 3 is a sign that the Civil War will play out on the big screen. Unfortunately, characters such as the X-Men, Fantastic Four and Spider-Man all play important roles in the comic book storyline, and those characters are contractually unavailable to appear in the Marvel Cinematic Universe at this time.

Downey’s participation in Captain America 3 was up in the air for several weeks, because while Marvel originally wanted him to play a small role in the film, the actor demanded more screen time and a bigger payday. Marvel Entertainment chief Ike Perlmutter reportedly ordered the screenwriters to write Iron Man out of the script entirely, but Marvel Studios president Kevin Feige worked the issue out with Downey’s reps at CAA so he could execute his vision for the future of Marvel’s Cinematic Universe. Sources say that Downey will earn around $40 million plus backend participation for the film, plus an additional payout if Captain America 3 outperforms Captain America: The Winter Soldier’s $714 million worldwide haul.

Both Robert Downey Jr.’s Iron Man and Chris Evans’ Captain America will next appear in Avengers: Age of Ultron, which premieres May 1, 2015.