Camila Cabello loves to explore. Whenever she visits a new city (which is a lot these days), she likes to run out and check out all the cool restaurants and shops, ride all the rides at the nearest theme park, and “go on, like, a crazy mountain adventure.” However, exploring new cities like a maniac while you’re also in the middle of two giant world tours (one with Taylor Swift and one to promote her own debut album, Camila) can present problems. For example, back in May, Cabello had to cancel a performance due to dehydration. Now, in August, at her doctor’s insistence, she is trying very hard to chill. Stay in her hotel and watch movies on her day off. Do a face mask. Relax. “I realized if I don’t take days off, I will actually die,” says Cabello, 21. “Or collapse, so I’m trying not to go too crazy for the rest of the tour.”

Dolce & Gabbana top. Sofia Sanchez and Mauro Mongiello

It’s late night in Pittsburgh, and she’s just finished singing “Shake It Off” with Swift and Charli XCX at Heinz Field. Fresh from the shower and dressed in a hoodie and sweats, her long dark hair combed over her shoulders, Cabello curls up on the couch, tucks her white-socked feet beneath her, and continues: “It’s hard, though. I’m at this point in my life when I’m so happy—it’s hard to say no.”

Anyone who’s heard Cabello’s sultry monster hit “Havana” (which, let’s face it, is everyone) knows she’s had a heck of a year. Camila won Cabello the Artist of the Year award at MTV’s Video Music Awards, and she also won for Video of the Year (for “Havana”). She picked up four American Music Awards in October, including New Artist of the Year. She’s pretty sure things are finally cool with her former bandmates in the girl group Fifth Harmony (after a controversial breakup two years ago). She’s in love with her boyfriend, British relationship coach Matthew Hussey. She just bought a house for herself and her family in Miami. Oh yeah, and “Havana” is now Spotify’s most-streamed song by a solo female artist in its history, with more than a billion streams.

Tre by Natalie Ratabesi dress. Sofia Sanchez and Mauro Mongiello

As Swift recently told a crowd in Miami, “She’s killing it right now, and she will continue to kill it. But beyond that, she’s one of the most wonderful people I’ve ever met in my entire life....She’s such a wonderful, incredible, honest, generous, graceful, hilarious, enthusiastic, childlike, and yet mature person, and I’m so happy she’s on this tour.”

It’s enough to make you hate her—except Cabello is not really someone it’s possible to hate. The child of Cuban-Mexican immigrants who fled Cuba when she was six, she grew up in Miami (her mom sold shoes at Marshalls; her dad washed cars), dreaming of auditioning for the Disney Channel. She hugs everyone she meets. She spends much of her free time hanging out with her 10-year-old sister, Sofia. Up until last year, the two shared a tiny lavender-and-pink bedroom with, as Cabello says, “Mickey Mouse all over it.”

When she was growing up, Disney World was not so much a place for Cabello as her personal North Star. It’s where her mother told her they were going when she loaded her onto a bus from Mexico City to emigrate to Florida. It’s also the place that made Cabello want to perform.“My friends and I all wanted to be on the Disney Channel growing up,” she says. “We all wanted to be singers.” The fact that Cabello actually grew up to be a singer, however, still seems pretty miraculous because, for most of her childhood, Cabello suffered from intense stage fright.

Basically, there’s the me that I really am, on the inside, which is the nerdy one—the kind of introverted, shy one—and then there’s the sexy, overly confident one, doing great dance moves and being super sassy.

In order to understand Cabello properly, you have to understand, first of all, that she is very shy—and also that she is a natural exhibitionist. Cabello loves nothing more than the idea of baring her soul, of sharing her deepest secrets with the world, but she also hates the idea of doing it in front of anyone she actually knows. “I had intense performance anxiety as a kid,” says Cabello, who arrived in the States speaking zero English and blasted her favorite pop songs from her boom box at school in an attempt to attract kindred spirits.

Dolce & Gabbana top and pants. Sofia Sanchez and Mauro Mongiello

But she also really needed to sing. So she practiced by doing karaoke to Britney Spears and Hilary Duff albums in the basement. Sometimes Cabello sang to a friend over the phone. Sometimes she sang through the closet door to her grandmother, but if that door opened, forget it. It was over. “I’m an introvert,” explains Cabello, who once turned down an offer to star in her middle school’s musical because the thought of singing in front of her whole school froze her heart. “I love any activity where I can observe and not necessarily be a part of it.”

Except, of course, when she’s in the middle of the spotlight in a tiny shimmery dress, dancing in front of thousands of people. “Basically, there’s the me that I really am, on the inside, which is the nerdy one—the kind of introverted, shy one—and then there’s the sexy, overly confident one, doing great dance moves and being super sassy.”

Cabello’s irresistible video for “Havana” nicely showcases these two sides of her personality. With her enormous liquid-brown eyes and voice that swings effortlessly from a deep, smoky growl to a breathy high pitch, Cabello is a temptress with a sense of humor, a geek unafraid to make fun of herself. The girl comes alive in front of the camera or when she’s up on stage in a packed stadium. She has what Simon Cowell calls the X factor, which is why, in 2012, when she was 15, Cabello convinced her parents to spend the money for her quinceañera celebration to drive her and the rest of the family to North Carolina to audition for Cowell’s show.

“There’s way less risk performing or exposing yourself to strangers than there is in your own town or school,” says Cabello, who felt trapped and miserable inside the inhibited persona she’d created for herself. “On The X Factor, I kind of became the person that I wanted to be. In interviews, I was super goofy and confident. I look at videos of myself from the first performance, and I’m winking and pointing. I was dying inside—literally, my hands were shaky, my voice would be flat allover—but I was like, I just have to just go for it.”

Chloé coat; De Beers necklace. Sofia Sanchez and Mauro Mongiello

Cowell knew magic when he saw it. Though she was rejected initially, he brought Cabello back as part of Fifth Harmony—which he first conceived as a sister group to One Direction. By now, the world is familiar with what happened between Cabello and Fifth Harmony. To put it bluntly, Cabello wanted more. She hated the groupthink and compromise of being creative with four other people (not to mention a herd of number-crunching A&R execs). She felt pressure to be sexy in away that she was not ready for, pressure to go along with the band, pressure to worry more about hurting people’s feelings than about making the best music she possibly could. “I would try to kind of rebel in my own way and wear turtlenecks or pants—which was allowed. Nobody ever put a gun to my head and was like, ‘You have to do this.’ But it was definitely moving in a certain direction and there was a group mentality, so you have to do it.”

“Camila is exactly what you see and know of her. She puts up no walls and hides behind nothing. She is 100 percent authentically her.” -Shawn Mendes

So Cabello went back into hiding, holing up in hotel bathrooms, feverishly writing lyrics while she was touring, and quietly collaborating with people like Shawn Mendes on the hit “I Know What You Did Last Summer” and Machine Gun Kelly on the hit single “Bad Things.” You can imagine how well that went over with the other Harmonizers. But the songs just kept pouring out. “Camila is exactly what you see and know of her,” says Mendes. “She puts up no walls and hides behind nothing. She is 100 percent authentically her.” Looking back, it all seems inevitable. The time had come for Cabello to break out. And of course her fellow bandmates weren’t going to like it. And of course, eventually, it would all blow over. “I think that we’re all good now,”says Cabello, some vestigial sadness registering in her eyes. “I saw Normani [Kordei] at the Billboard Awards, and we kind of mutually came up to each other. She’d performed that night, and so I was like, ‘Oh, how was it?’ She said, ‘Oh, I was so nervous.’ And I was like, ‘By next year you’ll be totally fine. You’re killing it. I’m so happy for you. I’m so excited to see what you do with your music.’ I told her, ‘I just want you to know, I really hope we can all move on from everything, and I’m genuinely happy for the other girls, and I hope you tell them I wish you the best.’ And she was like, ‘I’m so proud of you.’ It felt like everything is totally fine.”

For Cabello, the experience of going solo seems to have been mostly a huge relief. That’s not to say creating Camila was all flowers and light; there were still plenty of suits crowding around, trying to tell her what to do, and the song “Havana” was a nightmare to write. Cabello worked on it for five months. Eventually—in a moment of pure fairy-godmother-style magic—Pharrell Williams got in touch with Cabello’s producer Frank Dukes and asked to work with her. “It was my birthday, and I was like, ‘We have a chorus for this song, but I can’t figure out the rest,’ and he just came up with the melody for the verse we needed on the spot.” By the end of the day, the song was basically finished. But nobody at the record company wanted to make it a single. “They were like, ‘You have to make it faster. You have to add production. Radio isn’t going to get it. It’s a cool song, but it’s not your single.’”

Versace top; De Beers earrings. Sofia Sanchez and Mauro Mongiello

Swift, however, had other ideas. “She was like, ‘People on the outside are never going to think about the story that you want to leave behind,’” Cabello recalls. "‘That’s yours, so you have to always protect that, because to other people it’s a song, but for you it’s something personal.’" When “Havana” topped the charts in over 23 countries, she learned a very important lesson: “You just have to trust yourself. I’m never going to be like, ‘This is a huge song.’ But I really liked it, and that’s what matters.” It was a similar story, Cabello says, with the album’s second single, “Never Be the Same”—an impassioned torch song that she’s visibly proud of.“When I finished writing that song, I got the biggest song-ecstasy,” she says. “I was like, ‘I made something that sounded like the inside of my brain: the track, the words, the melody. This is what the inside of my brain sounds like.’"

He’s so similar to me. In person, we’re just weird and silly and stupid together. He makes me the happiest I’ve ever been in my life.

Cabello may or may not have written “Never Be the Same” about Hussey, but she freely admits that the worst thing in the world is when he’s in the audience at her concerts. “Any time he’s there, I get super nervous. I stutter or my hands are shaky,” she says, a rosy flare coming into her cheeks. The pair met on the Today set, but this is the first time Cabello’s actually named him or discussed him in public. “It’s annoying, because we’ve been together for kind of like a long time now, but every time, I’m like, ‘Oh my God, I have to talk now.’"

Otherwise, though, Cabello is completely nuts about Hussey. “He’s so similar to me,” she says. “In person, we’re just weird and silly and stupid together. He makes me the happiest I’ve ever been in my life.” Thankfully, Cabello’s family also approves of Hussey, because she’s with them pretty much constantly. “I’m super attached to my family,” says Cabello, who still sleeps in the same bed with her mother and sister when she’s not with Hussey and can’t imagine not living with them. Her mother accompanies her whenever she performs. You get the sense that Cabello’s family grounds her and reminds her of what’s important in life—but also that she’s increasingly aware of the importance of pleasing herself.

When asked about rumors that she’s going to star as Maria in Steven Spielberg’s upcoming West Side Story, Cabello says, “I don’t think so. I feel like this has been the first year and a half of me getting to know myself. I have this confidence now that I haven’t had before, of listening to myself and not really doing brain damage on ‘Should I release this song?’ ‘Should I do this this way, or should I do it that way?’ ‘Am I the way this person sees me, or am I the way I see myself ?’” Instead, Cabello says, she’s been locking herself away again, exploring ideas and writing lyrics and thinking about a new album. “I know exactly who I am, and I know what I want to do,” she says, smiling, “and I’m just not ready to give up that voice for something else right now.”

This article originally appears in the December/January holiday issue of Marie Claire, on newsstands November 22.

Lead photo: Johanna Ortiz top; De Beers earrings.