Los Angeles, March 13 (IANS): Actor Robert Downey Jr. became a real life superhero after he gifted a 3D bionic "Iron Man" arm to a little boy who was born with a partially developed right arm.

In a video posted on Facebook on Thursday, Downey Jr. dressed up as his fictional character Tony Stark to deliver a robotic "Iron Man" arm to Alex, who loves superheroes, reports aceshowbiz.com.

Alex was told he was meeting a bionic expert in a hotel room, but he had no idea it would be one of his favourite superhero characters "Iron Man".

"Nice bow tie, by the way. How were your travels?" Robert told Alex.

Alex replied: "It's very good." Robert then opened two cases, written Stark Industries, with one containing Alex's new arm and another one containing a larger arm for the actor.

Downey Jr. wrote alongside the video: "Had the absolute privilege of presenting a brand spanking new 3D-printed bionic Iron Man arm to Alex, the most dapper 7-year-old I've ever met."

The "Avengers: Age of Ultron" actor also shared on Twitter some photographs from his meeting with Alex. "Can't resist more pics from the #CollectiveProject. Special thx to Albert Manero, @MSOneNote, & @Marvel. #Limbitless," he captioned it.