When James Llewelyn Jones from Llanymynech found out he was going to see Coldplay perform in Cardiff, he knew it would be a day he would never forget.

But what James did not know – until the very morning of the sell-out concert – was that he would be joining the iconic band on stage to belt out the Welsh national anthem.

Unbeknown to James, as he got ready to set off for the gig on Tuesday, Coldplay lead singer Chris Martin had decided to plan a last-minute surprise for his Welsh audience with a rendition of “Hen Wlad fy Nhadau” to close the show.

The frontman urgently needed to enlist some volunteers to sing the anthem while he accompanied on the piano, and turned to Rhos Male Voice Choir, based in Wrexham. It was then that James, the choir’s conductor, received the call that was to flip his day upside down.

“I went to choir rehearsal last Monday and told a few people that I was going to see Coldplay,” said James, 39.

“Then on Tuesday morning, I was at my sister’s house getting ready to go and my phone rang. It was Geraint Phillips, the choir secretary, and he said we had just had the director of Coldplay’s management contact us through the website.

“They said Chris Martin is a huge fan of our choir, and has records of us, and wanted to replicate the way the choir sang the anthem.”

Geraint had told the band’s management that James was going to be at the concert with his family, and they asked if he would be willing to sing on stage. James agreed without hesitation, to the disbelief of his sister, brother-in-law and teenage nieces who he was going to the gig with.

James said: “My nieces, they are 14 and 17, were excited enough to be going! So when I said I was singing on stage they just didn’t believe me.”

Arriving at the stadium at 3pm, James and his family got to skip the queues that had been building up outside the venue since the day before. The VIP treatment didn’t stop there, with a front-row spot and invites to the afterparty thrown in to thank James for stepping up at such short notice.

James then took to the stage in front of the empty stadium with 19-year-old Elin Hughes, the other unwitting fan who had been roped into the performance, for a soundcheck.

“We both had a rehearsal on stage before the band got there,” said James.

“My nieces were in front of the stage and started going crazy. Next thing, I felt these hands on my shoulders, and it was Chris Martin. He said, ‘you guys are amazing’.

“We got to practice with the band and tried a few different things. It was a surreal experience.

“After the sound check rehearsal he came over and said, ‘this is magic, thanks for doing this’. Then he asked if we wanted to go back and do it again the next night!”

After a whirlwind day, it was soon time to enjoy the performance among the thousands of other fans before being called on stage to close the show.

James said: “This is something that I would never have dreamed to have done.

“I was brought up in Llanymynech and went to Welshpool High School, and music played a really big part in my life. My first experiences of music were through school.

“I was in the National Youth Choir of Great Britain, and went to Birmingham to study music at university. Then conducting took over. I was with the National Children’s Choir for about 12 years and I loved it, I thought, ‘this is what I want to do’.

“So even though I love singing, I thought I would never have the opportunity to do something like this.”

Returning to the Principality Stadium on Wednesday night for a repeat performance, James got to sing alongside comedian Rob Brydon and rub shoulders with the likes of Dawn French at the afterparty. But the best thing about the whole experience for James was the fact his family got to share it with him.

He added: “It was one of those surreal situations you find yourself in thanks to coincidence and chance.

“What made it for me was having my nieces with me and them being so excited – and to find out Chris Martin is a fan of our choir was amazing.”