US-ENTERTAINMENT-BAFTA LOS ANGELES JAGUAR BRITANNIA AWARDS-ARRIVThor better watch his back, 'cause his "friend from work" The Hulk has been spending a lot of time with Iron Man.

The other day, Robert Downey Jr. (Tony Stark/Iron Man) shared a bonding photo with fellow "Avengers: Infinity War" #sciencebros Benedict Cumberbatch (Doctor Strange), Benedict Wong (Wong, from "Doctor Strange"), and Ruffalo (The Hulk/Bruce Banner).

Ruffalo reposted that photo, writing, "Doing normal things with my not so normal Avengers brothers! This is not a La Croix ad." He followed up by sharing a new "Science Bros" photo with RDJ for National Selfie Day. Unlike the drinks photo, this one was clearly taken in the Atlanta studio -- complete with blue screen for later visual effects work:

#nationalselfie day. Science Bros Style. With the inimitable @robertdowneyjr

A post shared by Mark Ruffalo (@markruffalo) on

Ruffalo will next be seen in "Thor: Ragnarok," and the trailer showed that Chris Hemsworth's god is at least initially glad to see Hulk, his "friend from work" as a fellow Avenger. Hemsworth's hilarious recent Instagram video -- where he topples various Avengers action figures and mocks Captain America as an idiot -- spares The Hulk because "we're now mates."

But Bruce Banner and Tony Stark are the OG science bros (and the actors both starred together in David Fincher's "Zodiac" before becoming Avengers.) It looks like the characters will be spending even more time together in "Infinity War," which opens May 4, 2018 and stars everyone -- seriously, everyone -- in the Marvel Cinematic Universe.

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