Thursday on The Tonight Show Starring Jimmy Fallon, music legend Billy Joel and Fallon used an iPad and an app called Loopy HD to create a doo-wop group while singing "The Lion Sleeps Tonight."

"To sing with you is the craziest thing, and so I came up with an idea where maybe I can sing with you," Fallon told Joel. "... I have this iPad app, OK, it's called a looper and what it does is, it loops your voice. And maybe if we did this, do it right, we could be a two-man doo-wop group."

Apple CEO Tim Cook tweeted out Friday that the skit was "magical."

"Check this out," Tweeted Cook. "@jimmyfallon and @billyjoel with iPad and a cool app called Loopy HD. Magical."

Loopy HD is available from the App Store for $7.99. It requires iOS 5.0 or later and 14.4 MB. 

"Create music by layering looped recordings of singing, beatboxing, or playing an instrument with a savvy, sophisticated, tactile new looper that totally reinvents the formula," the app's description reads. "Loopy offers a sleek, expressive, instantly understandable interface that beginners can start using effectively straight away. It's fun, right from the start. More advanced users, however, will not be disappointed by Loopy's rich feature set, with extra features many other loopers just don't have."

Watch the video of Fallon and Joel singing below: