Robert Downey Jr. has joined "Captain America 3" after a number of rumors that the actor would return for a fourth Iron Man movie.

Variety reported that the actor would reprise his iconic role as Tony Stark/Iron Man and that he would play a key role in bringing the Civil War storyline from Marvel's comic books to the bigscreen. The company announced on Monday that the film would follow "Stark against Captain America's alter-ego Steve Rogers, played by Chris Evans, as they feud over the Superhero Registration Act, which forces anyone with superhuman abilities to reveal their identities to the U.S. government and agree to act as a police force for the authorities."

The company added, "Stark supports the program, but Rogers does not, saying it threatens civil liberties, causing sides to be taken and Rogers, among others, to go on the run to avoid arrest. The moral question and battle with his Avengers teammate essentially makes Stark a villain of sorts in "Captain America 3," providing Downey with a meaty role he could play out into future Marvel films, including a fourth "Avengers."

The plot seems to follow a different path from what many fans expected.

"Captain America: The Winter Soldier" had a number of questions unresolved, such as what would happen to the Winter Soldier, a.k.a. James "Bucky" Barnes (Rogers' friend-turned-foe), and if Cap's arch nemesis would return to join Captain America. Additionally, there was somewhat of a romance between Scarlett Johansson's Natasha Romanov/Black Widow and Captain America that never really got resolved. Also unresolved was Falcon's storyline and where he would fit in the Avengers films.  

With this new development, it will be interesting to see if S.H.I.E.L.D. returns and if Nick Fury and his team appear after they had such prominent roles in "The Winter Soldier."

The other question that many fans have wondered since the film was announced is whether Tony Stark's father Howard would return to play a cameo role. Dominic Cooper has been open to the possibility of returning to the franchise and this would give the series a great opportunity, especially with Howard's relationship with Captain America (although it woud be a challenge, especially considering that Howard is dead in the modern-day Marvel setting).

However, plot details are still very much under wraps. Downey Jr. was expected to quit Iron Man after the third "Avengers" movie, but it now seems that he will take part in the fourth film and it will center on his character's fallout with the government.

It is still unclear where in this franchise new heroes Doctor Strange and Ant-Man will fit and if the other heroes such as Thor, the Incredible Hulk, and Hawkeye will return. The "Guardians of the Galaxy"  is another series that Marvel has yet to reveal where they will fall in the Avengers universe.

Anthony and Joe Russo, who directed "Captain America: The Winter Soldier," will return to helm for "Captain America 3." The brothers are working on the script with Christopher Markus and Stephen McFeely. No other cast members have been announced for the film, but there are a number of crew members already assembled.

"Captain America 3" is slated for released in May of 2016.

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