“I fell on my ass in front of 80,000 people.” Shawn Mendes, singer, songwriter and 20-year-old budding superstar, sighs and pulls out his phone. “Look at this, dude.” The spill, immortalized on Instagram from the Festival d’été in Quebec last month, indeed lives up to the designation “most embarrassing moment” of his professional life so far. “I was excited and I didn’t see how high I was jumping from, and Dave Grohl was on the side of the stage, watching,” Mendes continues, mortified that the legendary Foo Fighters frontman and former Nirvana drummer witnessed the stumble, along with tens of thousands of fellow Canadians. “It was … amazing.”

If humility is part of Mendes’ career strategy, it’s working. But he immediately cues up another clip from the same festival shot the following night. During the Foo Fighters’ headlining set, Grohl tells 80,000 people: “Shawn Mendes is a bad motherf—er. You know why? Because he touched me.”

However indelicately phrased, this quote — which Mendes says he’s replayed “about a million times; it’s the coolest thing anyone’s ever going to say about me” — represents a crowning moment and a major step forward in one of the toughest transitions an entertainer can undertake: the perilous passage from teen star, particularly viral teen star, to career artist.

The failures, especially in music, are many — which former teen luminary has train-wrecked their way into TMZ this week? — the successes are few, and the “journey” is usually turbulent. Justin Bieber, Britney Spears, Christina Aguilera; even the seemingly bulletproof Justin Timberlake had to bob and weave explaining his role in Janet Jackson’s Super Bowl wardrobe malfunction 14 years ago.

But even by those measures, Mendes has reached high peaks in a fraction of the time — 15 billion streams globally, three No. 1 albums and three Top 10 singles on the Billboard charts, global headlining tours that have seen him sell out New York’s Madison Square Garden and London’s O2 Arena and perform for 120,000 people at Brazil’s Rock in Rio festival last year. He even played at Queen Elizabeth’s birthday celebration in April.

His origin story seems singularly unpromising in terms of longevity: He rose to internet stardom as a 14-year-old by posting dozens of six-second covers of songs by the likes of Bieber, Ed Sheeran and Adele on a long-defunct social-media platform, Vine. The video for his first proper single, 2014’s ironically titled “Life of the Party,” shows the fresh-faced teen walking balefully around a house party, feeling like an awkward outsider.

And yet four years later, his idols — Sheeran, Taylor Swift, John Mayer, even Elton John — are friends and/or collaborators, and his new album (which, in a clear signal of rebranding, is self-titled even though it’s his third studio LP) finds him branching into rock and R&B sounds, making a forceful play to expand beyond his initial pop, teen, female foundation to a global, adult audience.

“Mayer is such an incredible person to idolize,” Mendes says, “because he had an entire fan base when he was young, but now he’s 40 and all those people still love him but his music has transcended time and generations. It’s so impressive to be able to do that — to become something different without losing those people.”

Elton John is among those forecasting a similar career for Mendes. “For someone so young, he is remarkably accomplished and professional,” he tells Variety. “He has impressed me with his ability to grow as an artist on record, and especially live. A wonderful future awaits him.”

So what has Mendes done so right? Yes, he’s talented; yes, he’s almost classically handsome; and yes, he’s developed unusually fast in five years. But perhaps more than that, from his earliest days he showed a poise, a confidence and, not least, a fierce determination that sets him apart — not just as a performer but as a savvy public figure who knows how to cultivate and maintain a following by creating a connection.

By the time Mendes’ manager, Andrew Gertler, discovered him on YouTube early in 2014, the young singer had racked up nearly a million Vine followers and around 400,000 Twitter followers, all from his parents’ house in Pickering, Ontario. “I was immediately impressed by his voice,” Gertler recalls, “and I saw that he had extremely fervent fans who were so passionate and connected to him personally. But what struck me when I talked to him was how laser-focused he was. I had a Skype call with him and his mom, and he was so inquisitive and willing to learn. That humility — ‘How do I do this?’ — told me this is a once-in-a-lifetime artist, that this kid is going to do anything in his power to be great.”

With the support of his parents, Mendes quickly teamed up with the then-25-year-old Gertler, who brought his own network into action. Gertler’s friend, A&R rep Ziggy Chareton, was already on board: During college the two had interned at Atlantic Records for marketing VP Eric Wong, and by this point both Chareton and Wong were working at Island Records (and are now an executive VP and chief operating officer, respectively). While several labels expressed interest in Mendes, he felt a connection with then-Island CEO David Massey, who over the course of his career had worked with many young artists (the Jonas Brothers, Good Charlotte, Demi Lovato), and whose mother had managed teen singer Lulu. Mendes also showed more than a little shrewdness by playing a cover of Oasis’ hit “Wonderwall” in his first meeting with Massey, who had signed the British band to Sony in the 1990s.

“I knew in the first two minutes that he was a star,” Massey says. “When you’ve got that kind of artist you’ve got to think in the biggest possible terms, and that’s what we did from day one.”

Within weeks, the 15-year-old Mendes had thrown himself into preparing for stardom: As he finished his sophomore year of high school, Island released “Life of the Party,” and within minutes the song rocketed to No. 1 on iTunes. That success paved the way for his first major tour — a summer 2014 stint opening for teen pop singer Austin Mahone — during which he faced audiences of thousands armed with just his acoustic guitar. On the road, he first met his close friend and collaborator Camila Cabello, then a member of the other warmup act, Fifth Harmony.

“He later told me it was his first time really performing onstage, and his hands were shaking as he was playing the guitar,” Cabello tells Variety.

“I want to push myself to my limit and play as many shows and write as many songs as I can and fly around the world 10,000 times in a year.”

Yet he quickly gained confidence, and assisted by key collaborators who remain with him today — particularly songwriters Teddy Geiger, Scott Harris and Geoff Warburton — his first album, “Handwritten,” debuted at No. 1 on the Billboard 200 album chart in April 2015, and featured his breakthrough hit, “Stitches.”

Gertler considers the next move to be a major milestone in Mendes’ success: several months as an opening act on Taylor Swift’s “1989” tour, chosen by the singer herself. “On that first night, he was as nervous as I’ve ever seen him — ‘I’m opening for Taylor in front of 60,000 people a night in a stadium, and I’m just one kid with a guitar,’” Gertler recalls. But Mendes embraced the challenge and intently studied Swift’s set. “He watched every song, every show, imagining himself in that place,” Gertler says. “It was like seeing a mixture of a student in a classroom and someone really enjoying a concert. It took five or six shows for those nerves to go away, but I think it made him the amazing frontman he is now.”

That long view and hurricane-force determination have become hallmarks of his career. Asked why he thinks Mayer and Sheeran have embraced him, he says, “I think maybe John and Ed saw something in me that they had in themselves, which is a desire to be great. It’s not something you can acquire, and maybe it’s rare. I meet a lot of people who ask, ‘How do I do what you do?’ and within the first 10 minutes, from the way they talk about music, I can see that as much as they want to want it, they don’t. It’s just something you kind of have.”

Cabello has experienced Mendes’ commitment firsthand. “When we were on tour together, I never saw him,” she says. “He would go to his tour bus and practice guitar, then go onstage, and then go back and practice guitar. He’s the most dedicated, driven person I know.”

Peggy Sirota for Variety

Darcus Beese, who succeeded Massey as Island’s CEO last month, says: “The first time I met Shawn, I left thinking, ‘That’s the energy of a thousand suns!’ He left me both exhausted and exhilarated.”

Swift was the last artist Mendes would open for: He followed with his first headlining tour, which launched in March 2016 and continued across Europe and North America before wrapping six months later with his first sold-out date at Madison Square Garden. He quickly followed with his second album, “Illuminate,” which saw his lyrics and music maturing; the ensuing eight-month arena tour featured even more dates in Europe and Asia and his first show in South America.

As his following grew exponentially, Mendes spent countless hours cultivating it. “People forget how important groundwork is — physically being in every city, meeting people, like in a presidential campaign,” he says, adding that the interactions aren’t invasive. “I’ve known nothing but that since I was 15, so it’s not like I was at one time very private and now I have to be open. I’ve always been like that.* I don’t find it hard or disruptive, and I think I’m OK with it — until I’m not, anyway.”

Over the phone from Europe, Gertler says: “There are probably 600 fans outside the hotel right now, and he’ll stop and take photos and meet almost every single one, to the point where you’re like, ‘This is crazy!’ But he feels like he owes something to them — ‘I’ll take a minute or 30 minutes to make sure my fans know they’re appreciated.’”

Such a ferocious pace doesn’t allow much time for a private life, Mendes acknowledges. But he says that’s not the reason why he’s single. “I’m not currently dating anyone, but it’s not because I don’t have time — I don’t know if I’d be dating anyone if I was home in Pickering, either,” he says. “It hasn’t stumbled across me, and I’m not chasing it. Of course, seeing all those other artists and people in relationships, you think, ‘Maybe it would be nice; who would be great for me?’ And that’s when you realize: ‘This is wrong. Let it be. I’m not supposed to be with anyone right now.’”

One of the couples inspiring such thoughts could well be his friends Justin Bieber and Hailey Baldwin — the latter of whom he says is “one of the most beautiful souls I’ve ever met.

“It’s great to see two amazing people get together,” he says. “If you know them both separately it does make a lot of sense — a little bit of yin and yang.”

In the meantime, Mendes says, “I want to push myself to my limit of what I can handle and play as many shows and write as many songs as I can and fly around the world 10,000 times in a year, pushing myself to the point where it seems crazy. Ed did that and he’s doing that, and there’s something so exciting about pulling at that energy.”

Guiding him on that path is the practical advice of his mentor-friends. “Ed told me never to say no. He said, ‘Can you go to every radio station in America?’ And for the next two years, in just about every radio station in America, I saw a signed photo of him, like, ‘I’m watching you.’ Taylor told me to stop worrying so much about whether the audience is enjoying the show — ‘It’s not a singing competition, nobody came to not enjoy it, so you’re already up.’ And Elton is somebody who, no matter how successful, creative and praised he is, stays humble, and that’s a really big reason I don’t let the ego get to me.”

But asked where his drive, confidence and strong sense of self come from, Mendes pauses for a beat and replies with an answer that speaks to an unexpected vulnerability. “Insecurity of being not grounded?” he muses. “I have amazing parents and incredible friends, but just as much, it comes from being scared — fear of becoming the one thing everybody tells you not to be.”