The crowd at “The Tonight Show” had not exactly been prepped for Troye Sivan. The main entertainment was Jimmy Buffett, bluff and chortling, on hand to promote his feel-good jukebox musical. It was a mild March afternoon, and Mr. Buffett charmed the studio audience, even before he accepted a guitar and led them through “Margaritaville,” which everyone knew, chorus and verse, like a soused catechism.

Then, cutting through the margarita mistiness, appeared Mr. Sivan: a long-limbed elf with a wick of bleach-blond hair and the doe eyes of a Snapchat filter. As a panel of video monitors played behind him, Mr. Sivan vamped his way through “My My My!,” a thumping club anthem of undeniably sexual exhilaration, in a belted-and-buckled blazer that gaped open at the chest and closed around the waist, an outfit Grace Jones might have worn and enjoyed. Mr. Sivan stalked the stage like a supermodel in still-shaky training, his nipples peeking out as he danced. Margaritaville was in the rearview mirror, receding fast.

Hip-swinging pretty boys in eye makeup are nothing new; they’ve been singing on television since Elvis on Ed Sullivan. But Mr. Sivan is a creature of our time: a self-possessed, on-his-own-terms heartthrob, gay and untroubled, with the commercial sheen of a Disney star and the charisma of a boy prince.

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At 22, he has been famous for more than a decade, albeit in far-off corners of the globe and the internet. He sang his way into YouTubing, YouTubed his way into acting, grew up on webcam (he came out on vlog at 18), and now, ramping up to the release of his second album, is working hard to turn himself into a frisky pop phenomenon. With every TV appearance and video release, Mr. Sivan is barreling ahead, his identity worn proudly but easily. Are you ready, America? He’s Troye Sivan! He’s here, he’s queer and he’s used to it.