Taylor Swift regularly invited a wide range of surprise all-star guests onstage during her Red world tour, including Carly Simon, Jennifer Lopez and Fall Out Boy’s Patrick Stump. But as the tour wound down in London last February, she surprised fans by bringing out a relative unknown: British singer Sam Smith. Swift had discovered Smith’s song “Money on My Mind” via U.K. Radio 1 DJ Greg James on Twitter. Swift say,s “The hook sounded nothing like anything else I’d heard. I learned that he was a brand-new artist who hadn’t even been launched in the U.S. yet, but I felt this strange inclination to introduce my fans to him out at the O2 Arena. When I love something immediately, they usually react the same way.” Swift was right. Smith won over the crowd that night, and, driven by his hit “Stay With Me,” his album “In the Lonely Hour” has become a Top 10 hit around the world, selling more than 3.5 million copies.