The Only Christmas Song To Hit #1 On The Charts

Here's your question of the day: What's the only Christmas song to hit #1 on the pop charts? Did you guess Bing Crosby's 'White Christmas?' 'Rudolph the Red-Nosed reindeer?' 'Frosty the Snowman?' 'Rockin' Around the Christmas Tree?' Maybe Paul McCartney's 'Wonderful Christmas Time?'
All good guesses, but wrong. Read on.