Fucking hell, I didn’t realise that… Jesus Christ, that’s some club to be in! I’m going to have to phone my Mum up and tell her.”

I assumed that Niall Horan would have known that he’s among the elite group of Irish artists – U2, Hozier and Sinéad O’Connor being the others – to have topped the US Billboard album chart, but apparently not.

“So Enya hasn’t had a number one there or Van Morrison or Snow Patrol or The Cranberries? Fuck, it’s absolutely mindblowing to be on the list of people who have. It just shows what a tough country America is to crack. Whether they’ve got to number one somewhere or not, the production rate of talent coming out of Ireland – which probably has less people living in it than the borough of Wandsworth in London – is insane. I love draping the flag over my shoulders and being part of that.”

The enthusiasm level goes up another notch as he tells us about meeting fellow club members, U2.

“All of the U2 lads are brilliant. Bono left me a video recently. He’s very good at being nice to you. When I played the 3Arena last year, I walked into my dressing room and there was a letter that he’d handwritten – ‘Enjoy the night.’ He drew a little James Joyce-style picture of himself in the corner. Getting a letter from Bono the night I played the 3Arena for the first time on my own; they’re the things I’ll remember forever.”

While delighted to have done it multiple times with One Direction – “I’m still trying to process everything that happened to us,” he says – the feeling Niall got from his 2017 solo debut, Flicker, topping the charts on both sides of the Atlantic was extra special.

“The sense of ownership you feel when it’s your name on the cover and your stories you’re telling is incredible,” notes Horan who straightaway knew where he wanted to head post-1D.

“Hundred per cent. I know who I’m into and what my influences are and the kind of music that I want to play. The first four chords I learned were Oasis’ ‘Wonderwall’, so I’ve always loved that rocky band dynamic. I remember watching a guitar thing on American TV and Joe Walsh saying, ‘Every song should be written around a riff.’ Some of the greatest riffs you’ve ever heard are in Eagles songs, so he knows what he’s talking about. Another band that fits into that category is Fleetwood Mac. I was raging that I missed them in the RDS. My dad was there and said it worked really well with Neil Finn and yer’ man from The Heartbreakers.

“Anyway, there was no sitting around scratching my head and thinking, ‘What am I going to do next?’ I knew straight off what I wanted Flicker to be.

”That Horan is a Britpop child is evident from ‘Nice To Meet Ya’, the flagship single from his imminent Heartbreak Weather album, which wouldn’t sound out of place on an Arctic Monkeys album. No, really! From frisky (“I wanna blow your mind/Just come with me I swear/I’m gonna take you somewhere warm, you know j’adore la mer”) he goes into downright booty call mode on ‘Small Talk’, which crosses over into Prince territory.

“Guilty as charged,” he cackles. “I was trying to replicate the ‘Slow Hands’ vibe but with a bit more grit to it. If you listen to the album from start to finish, it’s me writing about a breakup from all the different angles. ‘Nice To Meet Ya’ and ‘Small Talk’ sit right next to each other because they’re very in your face, ego-driven lyrics. But they’re the moments you have when you go through a breakup. It’s not all sad, it’s like, ‘I’m fucking going out tonight, I’m going to paint the town red!’”

It can seem liberating but then a day later you’re crying into your beer.

“Yeah, and I did that! It’s not long before you’re, ‘Oh, I’m so sad… me, me, me’ again.’”

While the nods to Arctic Monkeys and Prince might only be in my head, Heartbreak Weather definitely sets out to emulate another of the all time musical greats.

“I wanted to write the ballad, ‘Put A Little Love On Me’, which was like my Elton John moment with the choice of chords,” he beams. “‘Still’ was another big one for me. I was trying to be self-deprecating but honest. Once you get them ones out of the way, it feels like the rest of the songs will come.”

‘Nice To Meet Ya’ and another of the album standouts, ‘San Francisco’, find Niall collaborating with one-woman Dublin hit factory Ruth-Anne Cunningham.

“I’ve known Ruth-Anne for years. She was mates with John Ryan and Julian Bunetta who did all the One Direction stuff. They were living in a similar area in Malibu and she was part of the 1D team. Ruth-Anne and me get on really well – obviously the Irish thing helps – so it was a case of, ‘If it’s not broke, don’t fix it.’ It seems like every time we get together we write something really good.”

I don’t have the Gok Wan credentials to tell whether the immaculately tailored check shirt he’s wearing today is one of Paul Smith’s, but Niall has become something of a walking billboard for the British designer whose 50 years in the biz bash he attended recently in Paris.

“Paul Smith is a fucking legend,” he enthuses. “He’s a fashion legend. He’s the greatest man that ever rocked the planet. He’s the nicest fella. He also makes phenomenal clothes. I had a really great time hanging out with Sir Ian McKellan who’s another fucking diamond and loads of young British actors like Jon Hamm and Mark Strong. There were people there I didn’t get to talk to like Anna Wintour who’s the godmother of fashion, isn’t she? Me going to fashion shows in Paris with Sir Ian McKellan… who do I think I am?

”The designer threads and equally expensive haircut aside, what’s striking about Niall Horan is just how unaffected by all of this he is. I’ve met pop stars who’ve felt the need to ram their success and wealth down your throat – according to the latest Heat Magazine Rich List, Niall is worth an extremely cool €67.7 million – but were you to run into him in Danny Byrne’s or the Number 1 (how apt) you’d think he was just a normal Mullingar lad out for a few bevvies.

“Stop it, you’re making me feel homesick,” he pleads as I reel off the names of his favourite hometown boozers. “There are nights when I’m in New York or Sydney or wherever and just want to jump on a plane back to Ireland to see my friends and family. The longer I spend away from Mullingar the more I want to come home. I’m going to make it a thing to get back a lot more this year when there are gaps in my schedule.”

Er, what gaps? Along with his considerable pop star duties, Niall is a partner in Modest! Golf Management, which looks after the likes of Ben Stow, Guido Migliozzi, Jack Singh Barr and Leona Maguire, and along with Cian Boylan and Niall Breslin a co-founder of Dublin 8’s Camden Recording Studios whose recent visitors include Loah, Hudson Taylor, Gavin James, Stephanie Rainey, Tebi Rex and Kodaline. And that really is just for starters.

“As I was saying earlier, this is a golden age in terms of Irish music,” Niall resumes. “Camden is the greatest studio in the country. We got that new desk last year and Bressie and the lads are running it really well on a daily basis. I’ve recorded bits of stuff there over the years, but never full songs or an album, which I’d love to do in Camden. The only danger is I’d be running round to Whelan’s all the time for pints!”

Niall had another pinch-me-am-I-dreaming moment before Christmas when he appeared on Saturday Night Live.

“To get that call from Lorne Michaels who started the show 45 years ago was insane,” he reflects. “For me, performing at the Grammys and doing Saturday Night Live would be on a par. Scarlett Johansson was the host, so it was a really good one to be on. I did it with One Direction back in the day, but was too young to realise what SNL is and the place it has in American culture. It’s like being Irish and appearing on the Late Late Show. Everyone you know suddenly goes, ‘Oh, he hasn’t been wasting his time!’ That’s one you get your granny up for.

”I’m not normally a man who’s prone to envy, but I’m green that Niall got up close and reasonably personal with Ms. Johansson.

“She was so nice,” he says making it even worse. “You give up pretty much your whole week for Saturday Night Live. As the musical guest, I got to perform two songs – ‘Nice To Meet Ya’ and ‘Put A Little Love On Me’ – and was invited to do a skit, which had me, Scarlett and one of the SNL regulars, Cecily Strong, as singing ghosts in a hot tub. I’m no fucking actor as you can tell, but I wasn’t turning that down. You arrive up on the Wednesday and do the camera block and the soundcheck. I got written into that skit so went back on Thursday and Friday to rehearse. You rehearse again on the Saturday when they’ve built the set and got all the lights in place. The whole hustle and bustle is crazy. You can sense that the crew has been doing it for a long time. The cameramen are New York dudes who’ve seen it all – and then some. You can feel the history and prestige of the show. It’s very much a ‘if these walls could talk’ type thing.”

Was he nervous following in the musical footsteps of such legendary SNL guests as REM, Tom Petty, Kendrick Lamar, Kanye, The Rolling Stones, David Bowie, the aforementioned Prince and Sinéad O’Connor?

“Aw, I was totally shitting myself,” he shoots back. “I’ve watched loads of those old clips on YouTube, so I knew how massive a deal it was. It was great, though. Another one I get really, really nervous doing because I watch it myself is Graham Norton. Trying to keep cool when you’re sat on a sofa with Olivia Colman, Helena Bonham Carter, Chadwick Boseman and Richard Ayoade is not easy.”

As you read this, Niall is locked into intensive rehearsals for the opening US leg of the Nice To Meet Ya world tour, which kicks off on April 20 in Nashville and finds his close pal Lewis Capaldi coming along for the ride.

“When Lewis was starting, he had a couple of little YouTube videos and songs released and a small number of Spotify listens so I reached out to him and said, ‘Love your fucking voice, man. It’d be great if we could write together or go for a pint or whatever.’ We had a few beers and became good mates straight away; it was probably the Celtic thing. We were like, ‘Fuck it; let’s go on tour together.’”

Lewis, the self-professed “man with the best nipples in the game”, has made some poignant contributions to Hot Press’ mental health specials.

“I don’t know about the nipples but, yeah, he’s been around stuff like that – we all have – and talks really well about it. The fact that everyone thinks he’s this joker makes it all the more powerful when he brings mental health up.”

Niall and his (for the time being) former One Direction bandmates always made it look easy, but being away from home at such a young age must have been tough at times.

“Yeah,” he nods. “I was having so much fun that I didn’t probably think about it, but in hindsight you’re like, ‘Jesus Christ, I’d loved to have gone home a little bit more.’ If you spend weeks and weeks on tour, there are going to be ‘I can’t be arsed tonight…’ moments. I’ve never been a crazy over-thinker. I’ve never had mad anxiety or anything like that, but I can understand why some musicians struggle with being on the road and the fandemonium. It’s the same for people in general; life can be fucking tough.”

Before if he was having a bad day there were four then three other lads to share the heavy lifting, whereas now it’s all down to Niall.

“To be fair, I’ve always had a really good team around me,” he says. “My parents and friends are on the end of the phone and come out on the road with me if they need to or I want them to. We met through an audition-type process, but having toured together I’ve become really good friends with all the lads in the band. Jake, who’s the same age as me, is one of the best guitar players I’ve ever seen. His taste, his touch and his ear are just insane. He’s become, along with me, our musical director and is really to the forefront when we play live.”

I was talking to another of Niall’s mates recently, Gavin James, who told me about the time he was given a lift back to Dublin in One Direction’s private jet.

“Did he mention that? Yeah, I was coming home for Christmas so I said, ‘Do you want to jump on?’ I don’t do stuff like that often, but when I do it’s nice to share it with people. Gavin and me have had a great time touring together. Gav’s fucking incredible. Great songwriter, great singer, great guy; I love him.”

He’s already listed a good few of them, but before we let him disappear into the Dublin night – a high-stool beckons somewhere near Grafton Street – what are Niall’s other wouldn’t swap ‘em for the world moments?“

Whether it’s Freddy Mercury and Queen at Wembley or Bruce Springsteen, who I’m a massive fan of, somewhere in New Jersey, the greatest moments in music have always been in stadiums,” he concludes. “I was lucky enough to go on a couple of stadium tours with One Direction and play to 80,000 fucking people at Croke Park, which was one of the best nights of my life. Right now, though, what’s most amazing is discovering that I’m one of only four Irish artists who’ve got to number one in America. I’m just going to make that phone call to my mum…”