Bressie leaves Roz behind as he sets his focus on triathlon
Niall Breslin (34) will be among 2,500 competitors taking part in the gruelling endurance test but he told the Herald he's "not worried at all".
The Voice of Ireland coach has been dating Roz (24) for almost two years.
But while his preparations for the race couldn't have gone better, the regime didn't suit Roz so he was training solo.
"We would do different types of training. She is so light and I'm so heavy we wouldn't be able to train the same way at all," he said.
The Ironman 70.3 consists of a 2km open water swim in the Irish sea, followed by a gruelling 90km cycle and then a half marathon (21km) straight after.
But Bressie said he's "not worried at all" ahead of his day of pain.
"It's just a really difficult challenge, it's the kind of thing where you have to remove yourself from your comfort zone and I've just always been that way inclined.
"I've always liked to push myself physically and that's what this is," he said.
While admitting that he hasn't done much running in the past, the cycling and swimming tomorrow should be a little easier.
"I've done a lot of work on the bike and in the pool so hopefully that stands to me. I only do it as a hobby so I'm not too worried," he shared.
Bressie is doing the challenge as part of his up coming documentary, Iron Mind, which he revealed will be released in early 2016.
The project follows four people with varying degrees of mental health issues as they take part in the Ironman challenge and how it affects their mental health.
The former Blizzards frontman has bravely spoken in the past of how he has suffered from anxiety and depression himself.
He's excited about the documentary project.
"I've a lot of interest in documentaries, it's very interesting and there are a lot of things you can explore," Bressie said.
He also said the fifth series of Voice of Ireland will be returning in January and that filming will begin in October.
"If I didn't enjoy it I wouldn't be doing it. I'm still enjoying it and it works well," he said.
However he confessed that he prefers documentary making because the talent show is "very formatted".
"With the Voice you know exactly what you are doing but with documentary you are constantly thinking on your feet."