Three years after sharing the screen on "Avengers: Age of Ultron," Marvel Cinematic Universe's smartest brains Tony Stark (Robert Downey Jr.) and Bruce Banner (Mark Ruffalo) are finally reuniting in "Avengers: Infinity War." However, those who are expecting things to go back to the way they were might be disappointed.

A lot has changed for both characters since they last met. Tony is at odds with some of the Avengers while Bruce is starting to permanently change into the Hulk. Speaking to Screen Rant, Ruffalo talked about how these events result in the different kind of relationship awaiting the brainy duo.

"Well coming out of Thor 3, Banner's had a life-changing experience in Thor 3 that makes him much more expressive and not so internalized, you know?" the actor said of his character. "So it's not combative but they're not so in-sync as they were. Plus, Banner doesn't understand Civil War. He just doesn't get it."

That said, fans can expect Bruce will no longer be that reserved character that lets leaders walk over him when he reunites with the team in "Infinity War." Both characters have plenty to process as well –Bruce on the conflict between Tony and Captain Rogers (Chris Evans), and Tony on Bruce and Thor's (Chris Hemsworth) absence. Despite these, Ruffalo assures they will still be working together throughout the third film.

"Oh yeah, there's great Science Bros. stuff in there, yes," he shared. "There's good Science Bros. stuff, too. We're paired up again."

Some images and bits of footage already teased the two's reunion but fans will have to wait a little bit more to experience what their relationship will be like. Fortunately, "Avengers: Infinity War" will now premiere a week earlier.

Originally scheduled for May 4, the movie is now set to open in theaters on April 27.