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Billy Crystal & Jimmy Fallon Sing 'Have Yourself A Merry Little Christmas' (VIDEO)

12/21/2012 12:55 pm ET | Updated Feb 20, 2013

Billy Crystal stopped by "Late Night" Thursday night to promote his new movie "Parental Guidance," but while he was there he was sure to go above and beyond the average duties of late show guest.

In addition to recreating the famous "Who's On First?" sketch with Jimmy Fallon and Jerry Seinfeld, Crystal picked up a microphone and sang a little something seasonal with the late night host.

Check out the full clip above.

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