Speaking with Brendan O’Connor on RTÉ Radio 1, Mageean said: "As an athlete, you're used to having an unsettled bowel.

“You train a lot, you're working really hard. Sometimes you'll go out on a run and you'll think, 'oh for goodness sake, I need the bathroom.'

"And you have to nip into a bush! Very much used to that.

"But it started to become a bit more frequent. I would get up in the morning and I would need the toilet four times. I thought, 'that's not normal'.

"I was feeling kind of crampy and was wondering if I had eaten something that upset my stomach. I kept finding logical reasons for it, which many people would. I thought, 'oh great, on top of everything else, I have an irritable bowel.'

It was only when her partner Tommy Moran suggested that it was something she should get checked out that she ultimately was referred by the Institute of Sport medical team to see a specialist at St Vincent's Hospital in Dublin.

"I'll never forget that day on the 20th of May. Going in to have what I thought was a routine little scope and I wouldn't find out results for a bit after. But instead on that very day, I found out that I had cancer.

"Because I'm so young and healthy, I thought I'll be at an early stage. Not that any stage of cancer is okay.

"I was sitting in that room with Thomas and Máire, my big sister, who came with me. My colorectal surgeon told me it was stage four. That the cancer was in my bowel and was quite significant in my bowel. It had spread to my liver and was quite significant in my liver. And there was a small amount in my lungs.

"Whenever he told me that, as silly as it sounds, my words were 'this isn't good, is it?'

"And he just shook and said 'no, it's not great. This is not a good diagnosis, Ciara.' This was the biggest blow to me. Finding out it was stage four.

"Me and Tommy sat in the car basically in a stunned silence and just began to cry.

"For the next few days, it was rough. Very emotional. Really unknown in terms of 'will I die in the next few months? Will I die in the next few years? Do I have longer?'

"I probably shouldn't have but I googled what was the survival rate for people with Stage four bowel cancer. I saw that it was 10-15% of the people who have stage four survive.

"I thought, 'okay, that's not good odds. I'm not a betting woman but I wouldn't have taken those odds for living.'

"But I did think, why can't I be in that 10-15%? That research is based on maybe an older population. I'm young and fit and healthy. I have no comorbidities. I can fight this.

"It's a strange mix of determination that I'm not going to let this cancer win but the sheer dread that the grim reaper was right behind me.

"I just completed my 18th round of chemo at the end of May. 18 really tough rounds. I have the side-effects on my hands. People are often surprised at how fit and healthy I look because I've gone through so much chemo.

"They question me about losing my hair. I've learned there are many different forms of chemo. Breast cancer patients often lose their hair but for me, neuropathy is the main issue, post-chemo. The situation in my hands and my toes is not what it was.

"The skin is coming off my hands. I'm very conscious I'm going to be doing book launches and shaking people's hands and hoping they're not going to be grossed out by the fact that my hands are in bits!

"But I'm feeling healthy. I'm hopeful that my prognosis can be good. At Christmas, I was told after my first 12 rounds of chemo that surgery wasn't an option and radiotherapy wasn't an option.

"And for the first time, I asked my oncologist, 'are we talking timelines?' At that point, he gave me the prognosis of two to three years.

"I walked out of that hospital appointment on the 24th December and I said, an expletive, I'm going to Costa Rica and I'm having fun.

"Because if I'm going to die, I'm going to fit as much living into the years that I have left. And that's how I feel.

"And I'm feeling hopeful. I randomly jumped on a support group call, the first I had ever done. I heard from a lovely lady based in Scotland who was diagnosed with stage four bowel cancer in 2016.

"I had tears in my eyes listening to her because, though she's still going through the toughness of monitoring and treating cancer, that was 10 years - not two or three.

"I don't know if fear is the thing I feel. Just complete sadness that I don't get to have what I had before.

"I was brilliant, I'm going to finish my career. Maybe me and Tommy are going to move out of our semi-detached. Maybe I'll convince him to move down the peninsula to Portaferry!

"That we'll start a family and I'll have kids. And they'll go through school and then university. And then I'll have grandkids and I'll get to be a granny. And I'll be bringing them as a parent and as a grandparent to all their sporting events. That I'll get to watch Tommy grow old and I'll get to have so many celebrations with my friends and family throughout the years.

"I get emotional thinking that I don't really have the luxury of thinking that anymore.

"It might be a reality if this treatment works. I'm hopeful that I get to live into old age, but the odds are stacked against me and that's really, really hard.

"I am so grateful for the support of the Irish nation. It's been there for me throughout my entire career. But I feel supported and loved throughout this journey."