In case you couldn't already guess, One Direction visiting 'Sesame Street' is about the cutest thing ever. In a newly released video, the guys teach viewers all about the letter "u" -- while spoofing their own hit, 'What Makes You Beautiful.'

One Direction first teased their appearance way back in January (doesn't it seem like ages ago?), but now we get to see their song in full. And, as expected, we're obsessed.

"This letter's 'u,' you know it's true," Liam begins. "It's starts some words. There are more than a few."

"Twenty-six letters are in the alphabet," Harry adds. "But we're here to sing about 'u'!"

So exactly what words do One Direction sing about in 'What Makes U Useful'? Well, let's see. There's ukulele, UFO, unicorn, uni-cycle and so much more! But don't worry -- the guys explain them all, with the help of some of the 'Sesame Street' characters.

See One Direction sing 'What Makes U Useful' in the video above!

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