Ferdia Walsh Peelo should currently be midway through transition year. Instead of attending classes at Coláiste Ráithín in Bray, however, he’s having a lot more fun jet-setting around the world. The flamboyant and friendly 16-year-old is sitting beside his Sing Street co-star, Lucy Boynton, on a couch in a Merrion Hotel suite, enthusing about the film’s Dublin premiere last night.

“It went great!” he says. “It was nice to bring the film home. We were really looking forward to it. I went to Sundance with it, and I went over to Toronto for it, as well. It had its Canadian premiere over there, which was really fun and it was received really well. We were especially excited for the Dublin one, though.

“That was my third time seeing it,” he continues. “Lucy had seen it twice before I had seen it. I saw it for the first time at Sundance, which was incredible. But last night was the most special time, because my whole family was there and all the lads were there. My brothers were there – it was an emotional night for us.”

Ferdia and Lucy play the lead roles of Cosmo and Raphina. Sing Street is Ferdia’s first ever movie. Six years older than him, London-born Lucy already has a few film and TV roles behind her (including playing the young Beatrix Potter in the 2006 movie Miss Potter and a significant part in the miniseries Sense and Sensibility).

“Yeah, I started out acting when I was like 11 or 12,” she explains, "and was kind of in and out doing it, trying to balance it with school and everything. But this is the first major one of this size. A role as unique as Raphina only comes around every so often. I feel extremely lucky to have been able to play her.”

For Ferdia, who is an accomplished musician, this is his acting debut. “It's my first acting role," he states. "I was a musician beforehand. I did my first singing competition when I was seven. I’m a classically trained singer. I did piano classically, as well. Then when my voice started changing and developing, I started playing different kinds of music and dipping into different styles.”

His musical ability is undoubtedly what landed him the gig. “I had a few bands then – and I landed Sing Street through an audition process when I was 14. It was an open casting in Dublin and that went great, obviously! There was a huge queue: I queued for ages, I got recalled and here I am now. I’m really lucky.”

Given that neither actor was actually alive in the 1980s, director John Carney gave them lots of musical homework to do in researching their roles. “It was a huge learning curve for both of us,” Ferdia admits. “We learnt so much about the ’80s and the music of that time. I watched lots of music videos.”

“Doing a film like this was such a good history lesson,” says Lucy. “It’s like a really in depth behind the - scenes history lesson, because it’s not only learning about the statistics and the facts of that time, Dublin in the ’80s and all of that, but also in terms of music and who these people are and their upbringing.”

John Carney also brought several Irish musicians onto the set. “John got loads of people in to jam out a few tunes,” Ferdia recalls. “Some real gems of the Irish music industry. Actually somebody who was in it, who passed away recently is Fergus O’Farrell [of Interference], who wrote a tune for the soundtrack called ‘Won’t Go Down’. It’s a really nice song that I recorded.”

The movie was shot over eight weeks in Dublin in 2014. Ferdia was just 14 then, and had to take some time out of school. So what did his Wicklow classmates make of it all?

“I think at the time they didn’t quite get it,” he smiles. “I mean it’s hard to say, because you don’t want to talk it up either. You don’t want to be that dick. It’s one of those things that you just have to wait until they see it. And then they realise...” Lucy laughs and finishes his sentence: “That you’re the central character in every scene!”

“Yeah, but they’re very excited for me,” he avers, modestly. “Friends change all the time. Some of the greatest friends I’ve got now are lads from the movie, because we’ve spent so much time together that we’re really, really close. Especially the guys in the band. We spent so much time together! That doesn’t happen with other films, apparently, so that’s what made shooting so special for us.”

Jack Reynor play’s Cosmo’s older brother, Brendan. “Jack is just amazing at the end of that film!” Lucy enthuses. “You read the script and you have a certain picture of the characters and what they’re going to be like. The way Jack has portrayed Brendan is so special. He actually is the heart and spirit of the film. I mean, I don’t want to give too much away, but him in the end of the film with his cheering just breaks my heart!”

Ferdia became close to him during the shoot. “He plays my brother. Jack’s actually been like another brother to me. We now share the same agent, so we have that connection too. He lives quite close to me, in Baltinglass in Wicklow – so that’s like a 20-minute drive from me. I haven’t actually been to his gaff yet, but he still lives really close. He’s lovely: I learnt so much from him and we became really close on set. Even just being on this promotional tour, he’s a great guy to be around.”

It was a very happy shoot, by all accounts. “There was a really great ambience on set for everyone involved,” says Lucy. “Everyone loved the script and it was a real passion project for everyone. So to come to work every day with that, with everyone wanting to be there, being so good and particular with their skill, it was a very unique experience.”

For her, the worst day was the one when she had to jump off Dun Laoghaire pier into icy cold water. Did they nail that scene in one take?

“No, oh no!” she sighs, laughing. “That would have been faaar too easy! And the last day of shooting was the final scene of the film, in the boat, and that was so intense. It was so choppy. We did half of that on the water and the other half was in front of a blue screen. With wind machines and rain machines! That was the hardest by far. And they had to use ice cold water because apparently it would have fogged up the cameras otherwise.”

Ferdia shudders at the memory. “Yeah, they would fog up even if it was just moderately warm. So they used freezing water. We had the worst brain freeze you could imagine! It was really intense – but it came across really well in the movie and that’s all that matters.” As to the future, Lucy already has stuff in the pipeline. “Yeah, I’ve got a couple of films coming out this year. One film called February, which is a horror film directed by Oz Perkins. I’ve just wrapped up another film called Let Me Go – and there’s a few other projects on the go.”

Ferdia is still on a break from school, but has already decided on his career path. “I’ve so many options, but I’m just waiting for the right role,” he says. “I’ve been bitten by the acting bug. It’s something I’ve learnt to love, so it’s been great. I’m also into music in a really big way, and that’s also something I’m definitely going to do. I’m only 16 so I’m taking a year off from school at the minute, because it’s only transition year for me, so I don’t know what I’m going to do. I’ve so many options – so I’m in a great position.”

Sing Street opens nationwide on March 18