Go Behind the Scenes of 'Avengers: Infinity War,' Where All of Marvel's Heroes Were Geeking Out (Exclusive)

ET was first on the set with Captain America himself, Chris Evans, as well as Chadwick Boseman, Scarlett Johansson, Mark Ruffalo and Sebastian Stan.

Avengers: Infinity War is set to be the most epic Marvel movie yet, if only because of its sheer size: The Avengers threequel has assembled some 64 stars -- among them a deep bench of A-listers from some of the biggest franchises -- for one massive team-up to mark the end of the Marvel Cinematic Universe as we know it. ET was first on the set when The Hulk found out he'd have to share the spotlight.

"No wonder I only have, like, four lines in the whole movie," Mark Ruffalo laughed. "We have to share it with all these other people."

Infinity War, arriving April 27, with an untitled fourth Avengers due out next year, sees Marvel's best and brightest unite to take on the intergalactic Mad Titan, Thanos (played by Josh Brolin). Which means that for the first time, Bruce Banner will rub elbows with not only Captain America (Chris Evans) and his Secret Avengers, but the Guardians of the Galaxy and the cast of Black Panther.

"I definitely geeked out a little when I was standing with them all," Danai Gurira, donning Okoye's traditional Dora Milaje armor, confessed. When Chadwick Boseman chimed in to confirm he'd witnessed it himself, Guirira exclaimed, "You saw me geek out? What'd I do?!"

When ET's Brooke Anderson arrived on the Atlanta set of Infinity War last June, Marvel's home base at Pinewood Studios had been transformed into the futuristic African country of Wakanda for a pivotal battle sequence. While much of this Avengers' episodes remains shrouded in secrecy -- even from the cast -- ET got scoop on some where Infinity Wars picks up with everyone, new looks (of Cap's new beard, Johansson teased, "He took prenatal vitamins, actually. That's a little known fact.") and unexpected superhero pairings.

"It's like the first day of school when you come back," Anthony Mackie, who dons his Falcon wings once again following Captain America: Civil War, deadpanned. "And then by the end of the shoot you want to kill everybody."

Check back all week for ET's full interviews with Chadwick Boseman, Chris Evans, Danai Gurira, Scarlett Johansson, Anthony Mackie and Mark Ruffalo, as well as Sebastian Stan (aka White Wolf) and directors Anthony and Joe Russo, discussing AVENGERS: INFINITY WAR, the Marvel movie 10 years in the making.