David Daly was 15 and loved hurling. He had played it two nights before he fell sick with a sore throat. David was tired, and found he had no appetite.
His concerned parents took him to the family GP, who ordered blood tests.
A week later, as the family drove home to Limerick from the graduation of David's sister Michelle, they were told to bring David straight into Limerick Regional Hospital.
The tests had revealed his platelet count was so low he needed daily blood transfusions.
Then came the news that "he had very severe aplastic anaemia; his bone marrow had shut down", his father Mike recalled.
"He also had a very severe nasal infection and the doctors were worried about it, because his white cells were not fighting infection and it was eating away at the back of his nose, close to his brain," Mike told the Sunday Independent.
That was in November 2011, and David spent that Christmas in Our Lady's Children's Hospital in Crumlin where he had a stem cell transplant under the care of Prof Owen Smith.
When Prof Smith asked David if he had any questions, it was "when will I be able to hurl again".
Mike added: "On day 18 and 19 post-transplant, there was terrible excitement because his white cell (count) started coming up.
"It was like winning the lottery really. From then on we were amazed at his progress. He was home after two months.
"His saviour was his sister Denise, who donated her bone marrow," he added.
Denise and Michelle (26) were both tested and Denise (20) was a 99.9pc match.
Denise recalled: "I didn't hesitate at all when I was told I was a match. We hoped that one of us was a match or else he would have been on a waiting list for a donor. It was a very happy day to be told I was a match.
"I was put under anaesthetic for the donation and when I woke up my back was wrapped up and I was in an awful lot of pain. I was sore for about two weeks. It was a very big relief that I could do this for my brother - I will hold it over him for the rest of his life!"
The siblings are very close, but Denise (20) said she would do the same for anyone else in the same position "because it is the most amazing feeling in the world to save someone's life".
Before the transplant, David had to undergo chemotherapy.
He lost his hair and a lot of weight and was prone to infections.
David, who is now 18, praised the staff at Our Lady's Hospital in Crumlin for their expert care.
He told the Sunday Independent: "Crumlin were great to me, they made it as simple as they could, but it was really frightening at the time because I didn't know what would happen.
"I don't think about it much now and when I do, I think how lucky I was. If it wasn't for my sister being a match I could have been waiting much longer.
"We go up and visit them in the hospital every Christmas now. I like doing it. It is the least I owe them and it makes me feel good."
David will sit his Leaving Cert in June and hopes to study sport and recreation in college.
He continues to play with his beloved U-21 Castletown Ballyagran hurling team in Kilmallock, Co Limerick.