EXCLUSIVE: Robert Downey Jr. Reveals His Secret Dad Superpower

This video is unavailable because we were unable to load a message from our sponsors.

If you are using ad-blocking software, please disable it and reload the page.

Robert Downey Jr. enjoys many powers vicariously through his character, Iron Man, but there's at least one real-life skill he has that not even Tony Stark can claim.

ET caught up with the Captain America: Civil Warstar at the Hollywood premiere on Tuesday night, where he and wife Susan dished on the Golden Globe winner's fatherly superpower.

WATCH: 'Captain America: Civil War' Stars Robert Downey Jr. and Don Cheadle Have the Best Bromance Ever

"He has an incredible skill of the best -- this is going to sound crazy -- baths possible," Susan told ET on the blue and red carpet. "He and our [4-year-old son Exton] take the most adventuresome, weirdo baths."

"Yeah, fun baths," Downey agreed.

While the action star gets into adventures with his son at home, his film alter-ego gets into an epic battle with his former ally, Captain America, in Marvel's latest blockbuster.

In the movie, a rift forms between Iron Man and Captain America (Chris Evans) due to political pressure to install a system of accountability for the Avengers.

WATCH: 'Captain America: Civil War' Cast Talks Hazing New Heroes and On-Set Dance Offs!

Evans puts on a brave face in the film as his character goes toe to toe with his friend-turned-foe, but last night he found his knees knocking at the gravity of how much the film matters to moviegoers.

"When you see fans come out and when you see how enthusiastic people are, you're kind of shaking in your boots about it," Evans told ET. "It's nerve-wracking, but it's exciting."

Captain America: Civil War opens May 6. Check out the trailer below!