Fans of Robert Downey Jr. are excited to see him return as Tony Stark (aka Iron Man) in Captain America: Civil War, in theaters May 6. The movie takes a look back into Stark's past, revisiting the tragic events that proved formative in his development as Iron Man. Now, RDJ is obviously a good-looking man at any age, but it's worth noting that in Civil War's flashbacks, he looks seriously young and dapper as a 20-year-old version of Stark. However, it's clearly still Downey Jr. himself, as opposed to a younger actor who was cast as a look-a-like. So, how did Marvel create the young Tony Stark in Civil War: Captain America? Was it makeup, CGI, or something else entirely?

At an April press conference for Civil War, director Anthony Russo discussed the scene, which he referred to as a "remarkable sequence." He said that they used CGI to create the appearance of Downey Jr. as a 20-year-old man, which was an incredible process but also extremely difficult. The director explained, "It took us months and months of work on that shot to make it work; it's very complicated taking the human face and changing the human face to make it look realistic. And in fact, it was the last shot that we completed in the movie."

Russo also acknowledged that part of the appeal of special effects-driven movies is that the technology is constantly evolving, so filmmakers are able to utilize new developments to upgrade the FX in their films. And Civil War is certainly no exception; the movie is jam-packed with special effects that are the products of the most cutting-edge CGI technology. From explosions to car chases to fight sequences, almost every aspect in the movie is touched some way by CGI.

One particularly interesting use of CGI in Captain America: Civil War is in the character's costumes. Filmmakers actually received some backlash for the appearance of some of the costumes, which fans deemed as looking too computer-generated. But although most of the actors on Team Iron Man sport costumes that are CGI, most of those on Team Captain America have "real" costumes — which, Chris Evans noted, was actually a giant pain when shooting high-energy scenes in sweltering weather. "Everyone was just dripping sweat, it was so humid and disgusting. Our bodies just became sweaty swamps," Evans told the New York Daily News.

Speaking of shooting, the studio actually released a video that shows what many of the Captain America: Civil War stunts look like when they're being filmed, and it's amazing how different the scenes look on set as compared to on the big screen. The actors run from gentle flashes of light that will eventually be giant explosions, and they execute fight choreography in front of green screens that will eventually be a backdrop of skyscrapers. The actual filming, therefore, is only a small portion of the production process. The CGI is what really brings the movie to life.

You'll have to decide for yourself how much you agree with the different uses of CGI in Captain America: Civil War, but all in all it looks like the special effects are pretty mind-blowing. And you have to admit that the use of CGI to de-age Iron Man into a young Tony Stark is a pretty novel concept. Although, as I said, RDJ is pretty great at any age.

Images: Walt Disney Studios (2)