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Can you imagine opening up your door to find Britney Spears and Ellen DeGeneres in full on Christmas Caroling outfits singing "We Wish You a Merry Christmas"???

I know a few people who'd faint right on the spot -- but luckily we won't have to imagine, the segment that Brit shot with Ellen last Friday airs on December 16th, according to Us!

And we think Brit and Ellen look pretty hysterical in their outfits...but did they actually sing? We love Brit's performances, but would be so great to hear her sing live!

Photo credit: Michael Rozman/Warner Bros