Robert Downey Jr. has once again suited up to play Tony Stark, the genius playboy billionaire-turned-superhero Iron Man — but this time, it has absolutely nothing to do with saving the world. Instead, theactor took the time to surprise a little boy with a special gift.

"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," Downey wrote on his Facebook page.

Downey was waiting for Alex Pring when he walked into a hotel room to receive a cosmetic "Iron Man"-themed upgrade to a bionic arm created for him by Limbitless Solutions. The company, a volunteer group started by University of Central Florida engineering Ph.D. student Albert Manero, uses 3D-printing technology to make free bionic arms for kids. Alex, who is missing his right arm just above the elbow, is a huge superhero fan and was apparently blown away to see Downey waiting for him.

"He didn’t question it much, so we kind of just went with it,” his mom, Alyson Pring, told CNN. "Afterward, I asked, ‘Why were you so quiet?’ He said, ‘I was freaking out!’"

According to Manero, Pring's new mechanical arm cost less than $350 in materials to create, much less than the tens of thousands the average prosthetic costs. Manero's goal is to reduce the cost even more and to distribute the inexpensive mechanical prostheses around the world. "We have had so many requests for new arms and people who want to join the project," Manero told CBC News on Sunday.

After their meeting, Downey invited Alex to hang out with him on the set of the new "Captain America" movie later this summer. No word yet on if director Anthony Russo plans on incorporating this new second Iron Man into the plot.

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Michael d'Estries ( @michaeldestries ) covers science, technology, art, and the beautiful, unusual corners of our incredible world.

'Iron Man' star Robert Downey Jr. delivers bionic arm to young boy
Alex Pring, a 7-year-old-boy missing his right arm above the elbow, received an unexpected visit by the actor last week.