Did the Russo Brothers Confirm a 'Surprise' Character Is Actually in 'Avengers: Infinity War'? (Exclusive)

ET sat down with the filmmakers on set to find out which Marvel character gets a 'very special arc' in 'Infinity War.'

"Joss Whedon used to get so mad at us," Scarlett Johansson says of the way the original Avengers director handled a large cast with a penchant for goofing off. "He was like, We're in the workplace! We were all just like, Doo doo doo."

The impending Avengers: Infinity War makes the cast of that first movie and that of the slightly expanded Age of Ultron look downright quaint by comparison, with 60-plus Marvel characters coming together for one monumental movie. And on the Atlanta, Georgia, set, the cast had nothing but praise for the brothers who were keeping it together behind the scenes: directors Anthony and Joe Russo.

"Thank God there's two of us," Joe told ET's Brooke Anderson. "When he's exhausted, hopefully I have energy, and when I'm exhausted, hopefully he's got some energy."

Infinity War marks the Russo brothers' third outing in the Marvel Cinematic Universe, following Captain America: The Winter Soldier and Civil War. "As people come in, it's great because they all bring different energy and new energy to the set," Joe said of getting to add even more characters to their sandbox. "It feels like there are a lot of variances as we progress through it, where we'll work with the Guardians for a few weeks and then we'll get to half the Avengers for another few weeks. It keeps it exciting for us and fresh."

One of the characters that the directors had yet to work with is Chris Hemworth's God of Thunder, who was sidelined from Civil War in lieu of his own solo adventure in Thor: Ragnarok. "Not having worked with that character in Civil War, as storytellers, we were even more excited to work with him in this film," Anthony explained.

"Thor has a very, very special arc in this movie that we're really excited about," he said. "I think Chris is very happy with what's happening now."

Another name came up in conversation, however, that we were not expecting confirmation of. Falcon himself, Anthony Mackie, let slip that some characters featured in Infinity War will be a "surprise," so we advise you stop reading if you want that surprise to remain unspoiled until you're sitting in the theater. The character in question was name-dropped when discussing the MCU's female heroes in this film. Here's what Joe Russo said:

"We have some great female characters in this: Captain Marvel is in it, Black Widow, Scarlet Witch. We have Wakanda coming in and there's a whole group of characters coming from the Wakandan universe, from the Black Panther universe -- amazingly strong characters, strong-willed characters -- and we have the Guardians. Two of the Guardians are daughters of Thanos, so there's a really strong connection to the main villain of the story. I think you'll see in the film that that they're very pivotal to the storyline, and I think the arcs are fantastic. We're really, really proud of being able to introduce Captain Marvel in this one."

Captain Marvel. As in Brie Larson's Captain Marvel, who will headline Marvel's first female-fronted film in 2019 and was spotted in costume filming on set in Atlanta earlier this year. Here is where things get confusing: Rumors that Captain Marvel would appear in Infinity War have been denied both by the Russo brothers and Disney. So, will she or won't she?

Well, there are a few different ways this could shake out: Optimistically, for people hoping to see Carol Danvers on screen ahead of her big debut next year, maybe the proof is in the soundbite. ("We're really, really proud of being able to introduce Captain Marvel in this one" sure doesn't seem like a slip of the tongue.) Maybe she's not in the film proper, but will make a cameo in one of the tightly guarded post-credit scenes, teeing up her solo film. Seeing as Infinity War and the untitled fourth Avengers, also due out next year, were shot back to back, maybe Joe meant that they were the first directors to work with Larson and "introduce" her into Marvel's cinematic universe. Or maybe it's even simpler: When ET visited the set in June 2017, maybe Captain Marvel was supposed to be in Infinity War but things have changed and now she's not!

We'll find out for sure when Avengers: Infinity Wars opens on April 27. If Captain Marvel is included, well, the Avengers need all the help they can get. "The Avengers are deeply divided. They have a seemingly irreconcilable problem," Anthony teased. "Unfortunately, that's the moment where the greatest threat they've ever faced comes up. It's a bad place for them to be in when that happens."

Be sure to check ET's complete coverage from our visit to the set of Avengers: Infinity War, including a by-the-numbers breakdown of the biggest Marvel movie yet and full interviews with the cast: