Ruffalo has been assembled with his many, many Marvel co-stars for a photoshoot, and shared the moment with his fans on Facebook – to the disarray of his nearby co-stars.
Brie Larson light-heartedly reprimanded him, as Vin Diesel gamely adopted his recognisable Groot voice.
“Hi everybody, we’re at the MCU photoshoot, there’s Vin D back there,” he said, revealing Diesel.
The latter star knelt down to the camera and said: “I sense there’s a day that’s gonna come where you’re gonna see Groot and the Hulk!”
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Samuel L Jackson then entered the shot and said: “What the f**k are you doing?”
“What do you mean, am I in trouble?” Ruffalo laughed.
“You f**king crazy!” Jackson yelled.
Ruffalo then revealed Evangeline Lily, who said: “This is supposed to be a secret!”
“You’re not supposed to do this,” added Larson, before turning away giggling.
“Oh s**t, I’m not supposed to do that,” Ruffalo grinned. “Am I in trouble?”
The team are currently shooting Avengers 4, with Infinity War reshoots expected in the new year.