In 1987, Sonny & Cher appeared on Letterman together. It was the last time the two ever sang together. They weren’t exactly best friends at this time, but they both knew it would make for an unforgettable moment, so they gave in to Dave’s insistence and sang the song together. And, it did indeed become one of the most unforgettable moments in late night TV history.
The performance wasn’t flawless, and they both looked noticeably uncomfortable at times, but in the end, this performance went down in history as one of the most memorable appearances of all time on Letterman.