Paul McCartney made a surprise appearance on The Tonight Show Starring Jimmy Fallon in 2016, lending his vocals to an all-star a cappella cover of his modern holiday standard "Wonderful Christmastime."

The performance, which you can check out below, came together as part of the promotional blitz for the animated movie Sing, which opened that weekend. Members of the movie's voice cast -- including Scarlett Johansson, Reese Witherspoon, Matthew McConaughey, Seth MacFarlane and Tori Kelly -- joined Fallon and the Roots for a Brady Bunch-style video that found McCartney taking the center square.

A Top 10 U.K. hit upon its initial release in 1979, "Wonderful Christmastime" started out as a non-album track recorded during the sessions for McCartney II LP. Later added as a bonus cut to a number of McCartney reissues, the song has grown into a yearly fixture on holiday radio playlists — reportedly adding roughly nearly half a million dollars to his annual earnings — and proven a popular cover choice for a long list of artists.

As fans are likely aware, McCartney's Tonight Show appearance wasn't the first time he's chipped in on someone else's rendition of "Wonderful Christmastime" — or even his first participation in an a cappella cover. He previously teamed up with the singing group Straight No Chaser for a version that appeared on their 2013 EP Under the Influence: Holiday Edition, which you can listen to below.

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