(CNN) -- Robert Downey Jr. may be Iron Man in the popular Marvel superhero films, but he recently dealt in some advanced bionic technology himself.
Downey recently presented a robotic arm to young Alex Pring, a Central Florida boy who is missing his right arm from just above his elbow. The arm was made by Limbitless Solutions, a volunteer group started by Albert Manero, a University of Central Florida engineering PhD student, to make free bionic arms for kids.
Through 3-D printing technology, Alex and others have had the chance to get a robotic arm so they can use their limbs again. Alex received his robotic arm in the summer, then later had it upgraded to resemble a "Transformers" arm.
This past Saturday, Alex received an even more impressive gift, from "Tony Stark" himself. Downey met with Alex in an Atlanta hotel room.
The actor showed the child two arms, one from Downey's movies and one for Alex: a real, working robotic Iron Man arm. As they both tried theirs on, they compared the lights inside their palms.
The video was posted Thursday by Downey as well as Microsoft, which arranged the meeting as part of its social media campaign, The Collective Project, celebrating students using technology to change the world. It very quickly went viral on social media.
Alex is 7, in first grade and a huge superhero fan. His mom told him they were going to Atlanta to meet Manero and a specialist who were working on a new arm for the boy.
"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!' "
After giving him the new arm, Downey invited Alex to hang out with him in Atlanta this summer when he's filming the new Captain America movie.
Manero met Alex through E-Nable, a volunteer network that matches people who have 3-D printers with children who need limbs. Alex's mom wanted to get him a replacement hand because he was being teased.
"Whenever people saw him, they'd say, 'What's wrong with your arm?' " Alyson Pring said. "Now it's, 'Your arm is amazing, you're so cool ... it helps educate people to maybe think twice before saying something like, 'Why are you like that'?"
The prop master for the Marvel movies built the case for Downey Jr.'s arm and the case for the little boy's arm. The college students made the actual arm for Pring, from the design to the painting to the robotics, said David Beauparlant, marketing manager at Microsoft.
"You couldn't even do this stuff not too long ago. It's amazing what the 3-D printing can do," he said.