Rex was born blind, with brain damage so severe his mother Cathleen was told he might never walk or talk or do much of anything, and yet he has talent beyond anything most of us can imagine.
60 Minutes was so captivated by Rex that we decided to follow him, to keep coming back to see what the years would bring. The last time Stahl visited Rex and his mom, he was 10. Today he's 13 and he's as joyful as ever.
But before you meet Rex today, meet Rex as Stahl first did.
Rex Lewis-Clack then, as now, was a study in contrasts: blind and full of enthusiasm, yet unable to dress himself, or even carry on a basic conversation.
But with everything Rex couldn't do, he could perform a musical feat. Stahl played him a song he had never heard, with his old piano teacher singing along. Rex, who can't see the keys, was able to replay the entire sequence, after hearing it only once.
Rex is a musical savant, one of a handful of people in the world who share a mysterious combination of blindness, mental disability, and musical genius.
But away from the piano, he was easily upset, confused by basic concepts, such as the difference between a square and a circle, and unable to find his way around the apartment he'd lived in his whole life.
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Music seemed to be Rex's only real connection to the world -- to normalcy. And the question was how far it could take him.
Now, five years later at age 13, he is playing Debussy for audiences around the country.
He's grown more than a foot since Stahl saw him last, and his technique on the piano has improved dramatically. But the answer to how far Rex has come is more complex, like the savant mystery itself.
Rex greeted Stahl with the same warmth and enthusiasm as ever. "Can I give you a big hug?" he asked.
But he seemed to forget that Stahl already knew his mother Cathleen.
Rex still has the magical ability to hear a piece of music one time and retain it, and he's taking that into a whole new realm by singing. Stahl watched as Rex's voice teacher Angela Rasmussen sang him a song he'd never heard before, Schubert's Ave Maria in Latin.
Stahl thought the song was upsetting Rex, since he plugged his ears and started making noises. But we were wrong - Rex played and sang the song, again, after a single hearing - in Latin.
Sara Banta, Rex's piano teacher, is pushing him to improvise and transform music into different styles, like asking Rex to play the song Blue Moon, which he'd just heard for the first time, in the style of Mozart.
"The more he improvises, he gets into new and wilder things which is fun for him. And it's creative," Banta explained.
Banta said she doesn't do that as much with other students. "They don't do it as well."
Rex was born blind, with a giant cyst in his brain. He developed severe autistic symptoms: small noises would make him scream, and he kept his hands balled up in fists.
"That became the way he would be," says his mother Cathleen, holding her hands up, clenched. "You'd have to peel his fingers open."