Ariana Grande covers Teen Vogue

Ariana Grande is backstage at Jimmy Kimmel Live!, and there's a problem. It's not a wardrobe malfunction, and it isn't her voice, either (she's fully recovered from a vocal-cord hemorrhage suffered in September). The issue producers are wrangling with is logistical: how to get the petite star on stage in a grande-size chicken costume without anyone spotting her. So much for glamour. Says the 20-year-old singer with a laugh: "I am the first in line to make an absolute fool out of myself."

There's nothing foolish, however, about Ariana's emergence this year as an undeniable force in pop music. Hollywood is littered with actresses who have fleetingly dipped a manicured toe in the waters of the music industry, but Ariana flipped the script with Yours Truly, pairing killer vocals with a hot R&B sound to earn a permanent spot in our hearts and iPhones. "The Way" was the song of the summer, and Yours Truly opened at number one on the Billboard 200 chart—something no female artist has done with a debut album since Ke$ha's Animal in 2010. If Ariana's relevance was at all in doubt, check out this endorsement from Katy Perry, who praised Ariana in a recent interview, saying she has "the best female vocal in pop music today." What's most surprising about Ariana's career: It's very possible that some of her massive fan base has no idea she's also the star of Nickelodeon's highest-rated live-action sitcom, Sam & Cat, whose episodes average 3 million viewers during the show's Saturday-night time slot.

The bit with the chicken suit goes off without a hitch. (When two superfans realize they've been standing next to Ariana for 10 minutes, the look on their faces is priceless.) Though for bigger laughs, Kimmel could have simply put a camera in her dressing room. Rocking five-inch heels and a sparkly skater dress, and seated alongside her date, The Wanted's Nathan Sykes (who'd just flown in), she settled her nerves by singing a theatrical version of Miley Cyrus's "We Can't Stop" in a voice that would be more appropriate on a Broadway stage than in a pop star's greenroom. "It sounded funny to hear 'we all so turnt up' in an operatic voice," Ariana says later. "I was making myself laugh so hard. I think I find myself funnier than everybody else might."

Ariana has always marched to the beat of her own drum, if not her own full electronic band. It's two weeks since Kimmel, and we're seated at a coffee shop near her home in Los Angeles while she talks about her unlikely path to stardom: the little girl with a big singing voice who made it all the way from Boca Raton, Florida, to Los Angeles, swapping Rainbow flip-flops for YSL heels while remaining true to herself. Acting was almost an accident. "When I was a child," she says, "the few things I watched were horror movies and Judy Garland films." But an open casting call led to a role in the Broadway musical 13 and then an invitation to L.A. Sipping an iced latte, she focuses those giant brown eyes and spells out her trajectory: "13, curtain call, L.A., the rest of my life, this interview."

To read more about Ariana's journey to the top and to get the inside scoop on everything from her dating life to growing up in the public eye, buy the issue on newsstands starting January 2.