He's the first artist to sell-out an arena tour before releasing an album. And yet even as his songs plunge into heartache and ennui, in person and online, Lewis Capaldi comes across as an agreeable rapscallion.

In his first major Irish interview, the 'Someone You Loved' singer talks about his irreverent humour, his hopes and fears for the future and why, if it all goes down the pan tomorrow, he'd be happy singing in a wedding band.

Lewis Capaldi is the latest boy next door to conquer the charts. He's also one of modern pop's foremost exponents of toilet gags and poo puns, as his 400,000 Twitter followers will tell you.

"I try to be honest about who I am and about what I find funny," Capaldi tells Hot Press. "As it happens a lot of my humour has to do with poo jokes. I'Õs not something I ever thought about - 'letÕs make this a thing'. But people seem to have grabbed onto it for some reason. Everything that has happened it me is so unbelievable that you're better off not trying to analyse any of it."

It's always a mistake to conflate the artist with the song. But Capaldi, who has just released his debut album, Divinely Uninspired To A Hellish Extent, is an extreme example. As a writer he bares heart and soul unabashedly. Take, for instance, break-out hit 'Someone You Loved' - written, among other things, as his way of processing grief over the death of his grandmother. Lyrically, melodically, in every way, the song is absolutely devastating. Capaldi has been likened to Adele and here the comparison makes sense - he's got a huge voice and what feels like a bottomless well of heartache. He performed 'Someone You Loved' on the final of Ireland's Got Talent and, amid the prime time tat and the cheese, it struck you straight in the solar plexus. And yet, in person he couldn't be further removed from the figure he presents on record. There's the 'poo humour' and general irreverence (!whoever says money can't buy ye happiness has never ordered three takeaways in one day," Capaldi tweeted recently).

Being Scottish, he has that instinctive Celtic insouciance too. He takes his music seriously - but can't bring himself to be po-faced in person. Also, he seems notably jittery about his career and how long it will last, theorising whether he might not end up living under a bridge if it all goes wrong.

"Sometimes there might be artists who have all the worries of the world on their shoulders," he says. "That's not me. I'm very honest in my music. I don't hold back. The thing is, it's all in the song. If you need to know my innermost thoughts that's where you will find them. I don't go around with all these troubles on my shoulders. I put everything into my songs. That's what they are for."

He has a few theories about his remarkable success - a progression that, in just two years, has seen him journey from headlining King Tut's Wah Wah Hut in Glasgow to selling out an Ireland and UK arena tour that includes a date at 3Arena in March 2020. Tickets are like gold-dust - remarkable in view of the fact that Capaldi is really only just getting started.

"I'm not a pop star on a pedestal," he says. "I don't try to be mysterious. That isn't who I am. There's nothing wrong with pop stars, don't get me wrong. Lady Gaga is fantastic. But I think people like the fact I'm approachable. There is no barrier between the audience and me. When fans meet and chat with me they understand I'm just a regular person."

It's hard not to see his rise as part of a wider trend. The bloke-from-down-the-road is the hot new thing in pop. There is Ed Sheeran, obviously the alpha and omega of the sloppy-shirted, Nando-patronising mega star. But also George Ezra, Ireland's Dermot Kennedy. Even Niall Horan from One Direction has reinvented himself as that guy you half remember from school who is suddenly on the telly, strumming a guitar.

"All music tends to have its phases," Ed Sheeran co-writer Amy Wadge ('Thinking Out Loud') told me when I spoke to her about the rise of the boy next door superstar last year. "We've had Britpop and the dominance of the bands for quite an amount of time. The boy with the guitar has always been there but Ed has probably blazed a trail. That has opened the floodgates...

"My theory is that because of the internet the easiest way to deliver a song is to sit in front of a webcam with just a guitar and a voice. That is the simplest approach and seems to be connecting with people."

Capaldi is part of that continuum, of which he seems quite aware. He wears his regular dude persona like a badge of honour. The last thing he would wish to be is regarded as mysterious and aloof. Who has time for that in their lives any more?

"Ed Sheeran once said that he would never turn down someone asking for a picture or an autograph. His logic is that if you doing a picture would make somebody's day, how could you possibly say 'no'. I agree with that."

He's met Sheeran a few times and will support him in the UK this summer. The truth is that Capaldi is rarely starstruck nowadays - though he was a bit nervous when he found himself next to Niall Horan in a London pub.

"I did think that maybe he would have an aura. But what you learn as you go on is that even famous people are really just people," he says. "They may be more recognisable. Under it all they're just like the rest of us."

It isn't lost on him how rapid his ascent has been. When his May 2017 single 'Bruises' went to number one on the Spotify charts, he was the first unsigned artist do so.

"It has been very, very strange," he says. "And things have really kicked up a notch since 'Someone You Loved'. I thought people who listened to my music would like it. I didn't expect to get new people. I thought, "this is a song that people who listen to my music will be into." I didn't think I would get any more fans than I had."

The power of the ballad comes from its universality.

"If people want to take it as a break-up song that's fine," he says. "But there are many ways in which we can lose someone. It could be someone dying. Or maybe you might have a falling out with a friend. I wanted it to be open to interpretation, so that people could draw their own meanings."

He had to fight to have it included on last November's Breach EP.

"It wasn't that the label was opposed to it," he says. "But we'd already finished the EP. And then we came back and wanted to put this song on. They were like, 'okay but it's going to be a lot of work at the last minute'."

Capaldi - who is distantly related to Doctor Who actor Peter Capaldi - grew up in Bathgate, a town of 20,000 in West Lothian in Scotland. His father is a fishmonger, his mother a nurse. There is absolutely nothing in his background to suggest a career in music, though from a young age he demonstrated a remarkable proficiency at singing and playing. He learned guitar aged nine and by 12 was performing in pubs (his first public performance was belting out 'We Are The Champions' at karaoke). His older brother had played guitar in bands and this stoked his interest.

The family would also take long drives from Glasgow to France for caravan holidays ("planes exist - why did we drive to France?... We didn't even bring our own caravan"). On those journeys his parents would play Queen, Genesis and Adam and the Ants - and it all soaked in.

"It's like anywhere," he says of Bathgate. "A wee bit boring. You spend your summer holidays doing fuck all."

Instead of doing fuck all he started writing songs.

"I didn't know if I was any good ... I just liked doing it," he said in a video interview last year. "I operate under that exact pretence today. I don't know if I'm actually any good But I like doing it.

"You don't know ... you could write the best song in the world by accident. You could be someone who is consistently writing amazing songs and one day you wake up and you never write another good song in your life. You never know... You could think you're writing the best song in the world. Some of my favourite songs have performed the least well. 'Bruises' was a song me and my managers never thought would be a best song at all."

As is now the convention he uploaded footage of himself covering artists such as The View (themselves former Hot Press cover stars) in his bedroom on to YouTube, and original songs on to SoundCloud. That was how he came to be discovered by manager Ryan Walter. "I was looking for something that I thought had the potential to go all the way," Walter told musicweek.com recently. "I wanted something with broad, mainstream appeal and when I found Lewis I was like 'This guy's voice, it cuts through'.... But whether or not I expected it to go this way, I don't think so - just because of how difficult it is to break new artists now."

The twist is that Capaldi looks and, in his conversation, sounds nothing like a conventional pop star. He feels this is part of his appeal. Walter agrees.

"Back in the day you had polished pop artists - that still exist - then Ed Sheeran, who was the first relatable everyman in the middle," he continued in his musicweek.com interview. "Lewis is almost a step further in that. His accessibility and relatability is resonating with people because they see a bit of themselves in him. And his awareness of who he is - just absolutely no fucks given - I trust him implicitly on that."

Such was Walter's faith in Capaldi that the singer and his team took the incredible step of announcing his arena tour, before the release of his debut album. "It's a massive statement and it's a statement I felt we could back up with the demand," Waler proffered. "People are desperate to see him and it was something we wanted to do to be like, 'Imagine playing to that many people without an album out. Imagine the possibilities...' It's a very surreal thing for us."

But the album is coming out and Capaldi is proud of it. He's also, it's fair to say, not too precious about the the toil that went into Divinely Uninspired To A Hellish Extent. As the title declares, this was a story of slog as much as inspiration.

"It's about hard work at the end of the day," he says. "You have to roll up your sleeves and get on with it. You can't just sit there waiting for the ideas to come to you."

Ireland has always embraced singer-songwriters and, in Capaldi's case, is once again to the fore. He secured his second chart number one here with 'Hold Me While You Wait', making this the first country where he's had back to back number ones. To celebrate he posted a video saying he could 'kiss Ireland on the lips - with tongues".

Among his early cheerleaders, meanwhile, were Dublin rockers Kodaline, who personally invited Capaldi to open for them at a sold-out show in Belfast last year. And he'll be in Cork this June as guest of Walking On Cars for their big open air gig at the Independent Park rugby ground. Growing up, Peter Capaldi was the famous one in the family. So Lewis was chuffed that the actor agreed to be in the video for 'Someone You Loved'. He did it as a favour too - Lewis may be a big streaming star but he can't yet afford a Hollywood level budget for his pop promos.

"My favourite role of his was in The Thick of It, where he played [vicious spin doctor] Malcolm Tucker. He's so funny - that's definitely my type of humour."

As Lewis says, the overnight nature of his success has caught him by surprise. His manager was slightly blind-sided, too, no matter that he saw huge potential in Capaldi.

"The way the first single came out and did so well... I knew it wasnÕt normal," Lewis says. "It almost helped... the fact it was so mental. If I was progressing from bigger gig to bigger gig or if the streams were progressing slowly, it would be easier to get caught up in it. I still live at home and then the song comes out and is a hit and it's just mental.

"The whole thing is so fucking crazy that I couldn't be caught up in it. I was just out of college and suddenly I'm flying to New York and LA to meet loads of labels. You have to remember this isn;t normal."

He doesn't want to suggest that life as a budding pop star is a lark. It is, sometimes. But there are negatives too.

"There is a lot of pressure," he says. "That's why a lot of young artists have issues with anxiety. You don't want to trivialise mental health issues but I have experienced panic attacks. Often it's a case of not looking after myself - drinking too much and then smashing loads of coffees to get through the day."

Capaldi admits he can become obsessed with negatives too. He may be selling out arenas and crushing it on the radio, but then a single may not succeed to the extent he hopes. Suddenly, he's up all night wondering what's gone wrong.

"It's human nature to focus on the downside," he says. "You need to sit back and realise it's all about finding a balance. That's what I've learned, anyway."

He's obviously uncomfortable being thought of as a celebrity. But increasingly he does get approached when out and about. A few fans even tracked down his parents' address and materialised at the end of the driveway.

"They told me they've seen a few people hanging about," he says. "I do still live at home. But I tour so much, that's the last place you're likely to find me."

Capaldi's determination to stay grounded is striking and it's tempting to conclude that, as the waters rise and he becomes genuinely famous, it is something to which he will increasingly cling. Being pragmatic and slightly pessimistic, he's even looked ahead and considered what he might do with himself if and when his music career sputters out.

"Definitely my ambition was to do something in music. I might still be a music teacher or in a wedding band. Who knows? What I really wanted was to play music and not have to get a real job - one I didn't enjoy and would be miserable in. I never expected my career to be this massive thing. It won't last forever and I'm totally cool with that. None of this is a given and I don't take it for granted."

Divinely Uninspired To A Hellish Extent is out now. Lewis Capaldi plays Independent Park, Cork with Walking On Cars (June 21); the Olympia, Dublin (November 21); and 3Arena, Dublin (March 8, 2020)