"It's all been leading to this," Stark says to Banner, in what is likely their first interaction in years. Banner disappeared from Earth at the end of Avengers: Age of Ultron, and was discovered by Thor (Chris Hemsworth) as living as a gladiator on the backwater battle planet of Sakaar.
The pair of Avengers share a moment together in what is likely Doctor Strange's Sanctum Sanctorum in Greenwich Village, New York, where a disoriented Bruce apparently crash landed in the debut Infinity War trailer.
Stark and Banner then head into chaotic New York streets alongside newound allies Doctor Strange (Benedict Cumberbatch) and sorcerer Wong (Benedict Wong), where they appear to set sight upon the cylindrical alien object investigated by Spider-Man (Tom Holland).
Lovingly dubbed the 'Science Bros.' since their meeting in 2012's The Avengers, where the pair bonded as the big brains of the team, Stark and Banner's friendship served as the basis for Iron Man 3's cheeky post-credits scene, which saw Banner play reluctant therapist to a talky Tony.
Age of Ultron pit the Avengers against one another when then-enemy Scarlet Witch (Elizabeth Olsen) used her abilities to warp Banner's mind, unleashing a savage Hulk on Johannesburg, South Africa. Hulk's rampage was thwarted by Stark, who was suited up in the Hulkbuster armor that was created by the duo in the event Banner ever lost control of his angry other half.
Bruce is in for a surprise when he returns to Earth after years away: the Avengers have since split, Captain America is a fugitive, and there's a massive alien invasion headed for the planet.
Infinity War marks the second chapter of a three-part arc for Banner, who is unable to headline his own solo movie because of an existing distribution deal with rival studio Universal. The arc, set into motion with Thor: Ragnarok, concludes in Avengers 4, out next May.
Avengers: Infinity War opens May 4.