Shawn Mendes is the red-hot poster boy of pop. His videos have been viewed 6bn times and he has more than 42m followers on Instagram. But don’t worry if you haven’t heard of him… just ask a teenager

Shawn Mendes is standing in his underpants in a suite on the fifth floor of a London hotel as a 200-strong crowd of screaming teenage girls gathers outside. “Everyone who doesn’t need to be in the room, leave the room,” he says politely but firmly, in a soft Canadian drawl. Pop’s current poster boy should be used to causing a stir. His #MyCalvins campaign (following in the footsteps of Justin Bieber in 2016) broke the internet earlier this year, inching the 20-year-old teen phenomenon – three US chart-topping albums, 30m monthly listeners on Spotify, more than 6bn video views – closer to tabloid supremacy and global domination.

At the Brit Awards that night, Mendes will cringe as presenter Jack Whitehall ribs him about “suspicious packages”, so it’s curious to hear him describe the Calvin Klein opportunity – and the subsequent results pored over by his 42m Instagram followers – as “a goal of mine at the top of 2018. As much as it’s a stepping stone for me to play a stadium, it’s a huge moment for me to step in front of a camera and take my shirt off. I don’t see one being less meaningful than the other.”

The air is thick with earnestness as we sit down for lunch in the hotel restaurant. I blurt out a question about whether he had to wear extra padding. “No,” he says, eyebrow raised. “They’re really good underwear.” Did they send you some free ones? “Yeah, I have boxes of them at home.” He lifts up the bottom edge of his T-shirt and pulls at the waistband of his underwear before quickly pulling his shirt back down. You’re not wearing them today are you? “Not right now,” he says sheepishly. “I should be.”

Facebook Twitter Pinterest Waking up with Shawn: Mendes famously has three daily rules – go to the gym, take two vocal lessons and never say no to a selfie with a fan. Photograph: Alex Bramall/The Observer

Mendes’s boy-next-door appeal and laser-guided ambition feels rather wholesome, with his sensitive, heart-on-sleeve pop-rock bops such as 2015’s UK chart-topper Stitches, positioning him as perfect boyfriend material in pop’s all important fantasy world. If Bieber is the unknowable loose cannon, then Mendes is pop’s picture-perfect head boy. But it’s clear that exposing himself so literally has its downside. “The last 48 hours have been so consuming, just reading what people are saying about me [on social media],” he sighs. Do you have to read it? “No, but there’s something about being human that makes you. I’m scared of social media and how much it affects me,” he continues. “It’s literally become infused with who I am.”

Last October he apologised to his 21m Twitter followers, claiming he was worried that what he was posting wasn’t meaningful enough. “For the first time I realised how many people are listening,” he says. He now monitors how often he goes online and tries to take regular breaks, using meditation to relax. “I don’t think of myself as conceited, but I definitely spend a lot of time reading about myself,” he says.

Mendes famously has three daily rules – going to the gym, two vocal lessons and never saying no to a selfie with a fan. He’s managed the first two so far and “took about 200 selfies yesterday”. Despite this, his rise has chimed with a shift in the upper echelons of pop – its recent exponents being anti-pop stars Adele, Ed Sheeran and (with her goofy dancing style and eternal quest for relatability) Taylor Swift, who’s now a friend. Even One Direction – whose blend of teen-orientated, guitar-led pop paved the way for Mendes – always felt like they were trying to play down the pop star element.

“The more open the world is getting, the more people are craving real,” he says. “I don’t think people want to see a made-up person. [In the past] there’s been a lot of dressing up, and I still think that stuff is amazing – like I’ll wear a sleeveless top – but at the end of it, when it comes down to you, I think it’s about being authentic.” For all this talk of authenticity and being like everyone else, I tell him, you’re also a pop star begging people to look at you. Do you have to believe your own hype? “Of course,” he says, his eyes darting over my shoulder to the mirrored wall behind. “You have to. If you wake up every day and say, ‘I’m OK,’ you’re going to just be that. If you wake up everyday and look at yourself in the mirror and say, ‘I’m great, let’s go sell out that stadium,’ then you will.”

Facebook Twitter Pinterest ‘They’re really good underwear. I have boxes of them at home’: Shawn Mendes in his Calvin Klein ad. Photograph: Calvin Klein Underwear

You could say he’s been in motivational training for a while now, having started out as a 14-year-old YouTube star, uploading acoustic covers of songs (Bieber, among others), before switching to the now defunct social media platform Vine. He taught himself to play the guitar via YouTube tutorials at home in the small town of Pickering, Ontario, while one of his first public performances was in a plaza in Portugal where his family – mum Karen, a British estate agent, dad Manny, a Portuguese businessman, and younger sister Aaliyah – were holidaying. While his parents were shopping, Mendes hopped up next to a statue and belted out a Bruno Mars song. “I was sweating and I thought, ‘Dude, if you want to be a singer, you’ve got to at least be able to stand on this statue and sing,’” he says of that moment.

Where was that pressure coming from? “It was from myself, which is pretty much a big statement on my personality at 14 years old.”

While he says he loved school, his early fame – after signing to Island Records his debut single, Life of the Party, was released when he was just 15 – meant he was bullied. “People were cruel at first,” he says, clearing his throat and fiddling with the rim of a cup of green tea. “They just thought it was so stupid.” He’d skip school every Friday to attend influencer events in which social media stars met fans who already assumed they were friends. “I was taking 1,500 selfies a night,” he laughs. “You quickly learn that what you love to do is a job, but I don’t resent what I do. I don’t hate taking selfies.”

Facebook Twitter Pinterest Dam buster: Shawn Mendes in concert, Amsterdam, March 2019. Photograph: Hollandse Hoogte/Rex/Shutterstock

Success was rapid, with his third single Stitches breaking the US top five and peaking at number one in the UK. That same year he supported Swift on her 1989 stadium tour. How did he cope? “This life is more real to me than anything,” he says. “If I were to walk down the street and no one recognised me, I’d feel something was wrong. When I was really young [fame] morphed who I was. If it was to become normal, it would feel un-normal to me.”

From the outside, I say, the other recent pop artists who can relate to that are Britney Spears or Bieber, people who have had issues with growing up in the spotlight. “A couple of times I’ve worried about that, too, but outside of all this I live a really normal life,” he says slowly. “You have to make an effort to carry your own bags, drive your own car and not be afraid of the public. I don’t blame people at all who stay inside. I understand how it could be terrifying to go to a restaurant and eat because you’re scared someone’s going to take a photo of you.”

Facebook Twitter Pinterest ‘I don’t think of myself as conceited, but I spend a lot of time reading about myself’: Shawn wears polka dot shirt by kooples.com and vest by sunspel.com. Photograph: Alex Bramall/The Observer

Is that more intrusive than a selfie? “I’ve been so lucky that fans have been taking photos of me eating since I was 15, so I’m a little bit numb to it,” he says, his tone rarely deviating from preternaturally calm. There’s probably an Instagram account called Shawn Mendes Eating, I joke (I check later and while there’s no account, there is a hashtag to follow). Can it feel as if he’s being watched? “I’m inherently [aware of] that all the time.” If it ever gets too much, he leaves rather than making a scene. Are you a people-pleaser, I ask? “Yeah, is that bad?” he smiles. “It can lead to failure, but if I fail trying to please everyone, then that’s OK.”

Mendes spends a lot of time contemplating people’s perceptions of him. Last year he publicly criticised a Rolling Stone cover story, expressing his regret that “the positive side of a story doesn’t always get fully told”. I assume it’s because the piece mentioned his penchant for smoking weed, a detail that had upset some fans. “That didn’t bother me,” he smiles. “Actually, I was happy about that because maybe it’s OK for them to understand that weed’s not a big deal.” He says he hasn’t smoked in three months.

Another part of the story focused on rumours about his sexuality. “For me it’s hurtful,” he says. “I get mad when people assume things about me because I imagine the people who don’t have the support system I have and how that must affect them.” (In late 2017 he posted an emotional Snapchat story: “First of all, I’m not gay. Second of all, it shouldn’t make a difference if I was or wasn’t.”) He sighs and says: “That was why I was so angry, and you can see I still get riled up, because I don’t think people understand that when you come at me about something that’s stupid you hurt so many other people. They might not be speaking, but they’re listening.”

Facebook Twitter Pinterest ‘If I were to walk down the street and no one recognised me, I’d feel something was wrong’: taking selfies in Toronto last summer. Photograph: Michael Hurcomb/REX/Shutterstock

He says the reason he criticised the article was over a small detail in which he mentioned Dua Lipa and her boyfriend, and how amazing it looked to be in love. “It made me seem so creepy,” he says. “If anything, the article made me realise your career isn’t over if people think you’re not perfect.” You could see how the creepy singleton tag might irk him, and also why it might stick – a lot of Mendes’s biggest singles play on the idea of him as the emotionally needy bloke who gets messed around and comes back for more.

Are you bored of being The Nice Guy? He splutters, clears his throat and sits bolt upright. “Yeah, I am! It sounds so stupid – to be a nice person is the best thing in the world – but, yeah, I’m 20 and I just want to have fun. What I don’t want to do is live the rest of my life thinking, ‘I wouldn’t do that because I’m known as Prince Charming.’ The second that someone corners you into a personality, you don’t want to be that person any more.”

Two weeks later, Mendes is onstage in Amsterdam. In keeping with the floral artwork for his recent self-titled album, a 50ft rose snakes up to the ceiling from the so-called B-stage where he’ll later serenade the throngs of teenage fans and nodding dads with a handful of ballads. Replica light-up roses (€20 a pop at the merch stand) bob about in the dark as Mendes runs through a hugely entertaining, PG-13 simulacrum of a rock show to ear-bleeding screams (“God I’m so old,” a woman sitting behind me yells as she surveys the crowd).

Facebook Twitter Pinterest ‘Your career isn’t over if people think you’re not perfect’: Shawn wears a shirt and trousers by givenchy.com. Photograph: Alex Bramall/The Observer

Keen to further align himself with the pantheon of rock’s smiliest exponents, tonight Mendes segues from a cover of Coldplay’s big-hearted anthem Fix You into his own, the Kings of Leon-esque In My Blood, a song that surprised fans by touching on depression. Tonight it’s transformed – with the help of a ticker tape explosion – into something close to catharsis.

“There’s nothing like being on stage – you feel like Superman!” he’d said earlier, claiming it to be better than sex or any high. “My goal now is to enjoy what I do more and more because otherwise it doesn’t fucking matter. I used to think it was all about the crowd, but I have to be happy within myself.” As he takes his millionth selfie, his face radiating pure elation, you believe he might be.

Shawn Mendes plays London O2 on 16, 17 and 19 April

Fashion editor Helen Seamons; grooming by Anna Thompson using Bobbi Brown and Monat; lighting by Michael Furlonger and Tilly Pearson; digital operator John Munro; fashion assistant Penny Chan; shot at 12th Knot, seacontainerslondon.com