The Tonight Show host, 42, returned to host the NBC late-night sketch comedy show for the first time since 2013 to celebrate the first-ever episode that aired live from coast to coast. "Tonight is bigger than a show," he said during his opening monologue. "It's a party!"
SNL's house band then began playing "Let's Dance" as Fallon walked off the stage and through the halls of the studio, surrounded by dozens of backup dancers. While he sang the 1983 tune, he was joined by the SNL cast members and the evening's musical guest, Styles, 23.
And while the former One Direction singer only appeared for approximately 15 seconds, his charming (and funny!) dance moves and irresistible smile essentially stole the show.
Later on, Styles performed his new single, "Sign of the Times," and debuted a second song, "Ever Since New York," from his upcoming debut self-titled solo album.
Saturday Night Live airs on NBC Saturdays at 11:30 p.m. ET.
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