In one of the most important Marvel pieces of news of all-time (yes, even bigger than when they announced that an Avengers movie was happening), it has been revealed that Robert Downey Jr. has joined the cast of 2016’s Captain America 3. What’s the big deal? Well, the movie will kick off the famous Civil War storyline!

For those of you unfamiliar with the seven-part series from Mark Millar and Steve McNiven, it pitted Captain America against Iron Man in a war which saw the heroes of the Marvel Universe split off into two factions. Why? To battle it out over the newly implemented Superhuman Registration Act, a bill which required them to reveal their identities to the government, something Steve Rogers was not willing to support.

Captain America 3 will follow the Civil War comic closely, setting up a new wave of Marvel movies for the next seven years. Downey was originally set to only play a small role in the threequel, but after some lengthy negotiations, he’ll pick up an extra $40 million (and backend) for once again playing Iron Man.

In fact, his role in the movie is now major and will apparently see him portrayed almost as a villain, just like in the comic books as he sides with the government and goes after Captain America and his rogue team.

Here’s a rough synopsis of sorts from the site that broke the news, giving us a better idea of what to expect:

“The plot will pit Stark against Captain America’s alter-ego Steve Rogers 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. 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.” Now can you see why this is such a huge deal for Marvel?

It’s pretty close to the comics, though some changes will likely be made along the way, especially if Captain America 3 is setting up Civil War for a future Avengers movie (which seems the most likely option here).

Either way, there are big things in store for the Marvel Cinematic Universe, and we’ll keep you updated!