He tells the Irish Times: "It was in the summer of 2014 at the Los Angeles Forum. We were on tour with Kiss and I was having chemotherapy at the time, scheduling my treatments around the shows and the travel.

"It was one of the three regimes of chemotherapy that I had gone through over the last several years, but this was a particularly brutal one. It was called Ice - named after the combination of drugs used: ifosfamide, carboplatin and etoposide.

"I don't remember a thing about that show, but I do know we had to cut out a few of the songs as I sing a lot of the high parts and there was no way I was going to reach those notes that night. I've no idea how we got through it, but somehow we did."

He continues: "I had been at hospital the whole night before this show getting an infusion of Ice. I didn't realise it at the time, but it turns out I had a bad allergic reaction to one of the chemotherapy drugs.