WATCH: Robert Downey Jr. surprises 7-year-old boy with bionic ‘Iron Man’ arm

Actor Robert Downey Jr. became a real-life superhero to a young fan when he helped deliver a bionic arm to a seven-year-old boy named Alex.

The heart-warming video of the event posted Thursday shows an unsuspecting Alex, born with a partially developed right arm, being led into a hotel room where he is greeted by Downey dressed as Tony Stark, Iron Man’s alter ego.

As Alex enters the room, the superhero fan can’t stop smiling as he greets the actor with a handshake.

“Nice bowtie by the way,” says Downey, who then unveils to Alex his new bionic arm, as well as an Iron Man model for himself.

Asked if he knows who he’s meeting, Alex grins before responding with “Iron Man,” as The Avengers actor pumps his fist in the air. When asked if he knows Iron Man’s name he says “Robert,” which again brings another round of laughter.

WATCH: Chris Pratt, Chris Evans surprise children at Seattle hospital

The arm was designed by Albert Manero, a Fulbright scholar and doctoral student in mechanical engineering at the University of Central Florida, who founded the company Limbitless Solutions which builds affordable, bionic, 3D-printed arms.

The arm cost just $350 to make, according to Microsoft’s The Collective Project, which showcases the work of students making positive changes for their communities. A similar prosthetic can come with a price tag of more than $40,000.

The video shows Downey and Alex trying on their identical “Iron Man” arms with the actor joking: “Half the time I design one of these, it winds up breaking on me.”

“But what I keep doing is working on it, kind of like how you’re working on it with Albert,” he added.

“He keeps working and working until he gets it right,” Alex responded.

Downey posted the video to his Facebook page, where he wrote: “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.”