As for going the whole way to the final and winning the show, Nellis said he is just taking it week by week.
“I remember saying to my wife before I started ‘I would love to get through week one, I just don’t want to be first out’ but even if I am first out, even being invited, I’ve already won. So, the goal right now? I just want to come out and say I’ve given it everything I have.”
Nellis says he has no grand visions of winning but admits he’s starting to feel the pressure of making his family’s weekends.
“It didn’t really land on me until a week or two in just how much it really meant at home. I have a huge family, I have like 30 cousins on my dad’s side alone, a typical Belfast Irish big family.
“So, there are a couple of hundred people who sit down every Saturday night, and I now make or break their Saturday night,” he said.
“Outside that, the town I’m from, they’re showing it on screens in all the bars, and I think across Northern Ireland there’s a lot of support.
“I’ve been blown away by it, but I also feel that responsibility to have fun.
“It’s almost way bigger than just me and how I feel. It’s how hundreds or thousands or tens of thousands of people feel.”
You can watch John and Katya in action on BBC One at 18:15BST on Saturday night as they take on Icons Week, with routines inspired by some of the best-loved recording artists in history.