Earth's Mightiest Heroes have seen nothing of The Hulk since he took a Quinjet ride at the end of Avengers: Age of Ultron which ended in him being stranded on Sakaar. The Jade Giant is, of course, coming home in Avengers: Infinity War and it sounds like he knows a lot about The Mad Titan.
"Once again, I think he’s trying to find his place in the line-up," Mark Ruffalo explained during an on-set interview. "He’s having some difficulties integrating with the rest of the group, but he’s also privy to some information that is essential for their survival… Banner knows probably more about Thanos than probably anybody and he’s really trying to impress on everybody how dangerous he is."
How does Banner know so much about Thanos? Well, it's presumably because he crossed paths with the villain when he attacked Thor's spaceship, a moment first teased at the end of Thor: Ragnarok.
So, what does the hero make of his foe? "The Hulk is also mightily impressed by Thanos."
As for how Banner is going to react to finally being reunited with Black Widow, it sounds like we can expect the divisive romance to continue being a big part of each of their respective arcs here. "They’re star-crossed lovers. So it’ll be something they’re dealing with for the rest of their living days I think. Whether it’s requited or unrequited, I don’t imagine that’s gonna go away any time soon in one iteration or another." Will there be time for romance during Thanos' attack on Wakanda, though?
Probably not but Ruffalo has previously teased that Thor: Ragnarok, Avengers: Infinity War, and Avengers 4 serve as a trilogy for the Jade Giant, so we'll more than likely get a resolution here.