Father's Day is extra poignant for singer Dave Maher who lost his son to cancer 11 years ago

Musician Danny was just 20 when he died 11 years ago.

His three younger sisters are continuing his legacy by singing in a band with their dad and were chosen to perform the main theme song for World Earth Day, which was recently broadcast to 190 countries.

Lullaby For the World went to No2 in the Irish download charts and was co-written for the family by renowned songwriter Brendan Graham, who famously penned You Raise Me Up.

Dave's three daughters Stacy (20), Robyn (18) and Ruby (13) hail from Newbridge, Co Kildare.

The two oldest girls play guitar and piano and attend the prestigious Laine Theatre Arts in England, which Victoria Beckham went to, while Ruby appeared on The Voice UK Kids show and was picked by Will.I.Am to be on his team.

Ruby sings lead vocals in the family group, with Dave playing guitar.

But they never forget Danny, who Dave got to join his original band when his son was 14. He had been taught to play the guitar from the age of seven.

"He was a fantastic character," recalls Dave. "Everybody that met him, he made an impression on them. I think God just wanted him. He's minding us and he's looking after us on our way."

Danny developed a lump on his forearm and on his 18th birthday he got the results of a biopsy and was told he had synovial sarcoma, which is a rare type of cancer that strikes teenagers in particular.

"It was awful though, because the tumour grew and cracked the bone in his forearm," sighs Dave. "We had to amputate his left arm, which he played the guitar on.

"We were trying to comfort him by telling him 'it's your right arm that makes all the chords', and that maybe he could get a prosthetic left arm and strum with that."

Danny had several months of chemotherapy.

"The professor called us in one day and said: 'I'm sorry to tell you this but there's nothing more we can do for your son, we have tried all the different courses of chemotherapy'," remembers Dave.

He and his musician brothers and others involved in the showbiz industry raised funds to send Danny to a specialised cancer hospital in Germany.

"We went for some experimental treatments in Dresden," he explains. "I just slept on the floor in the hospital.

"We had to try and stop it from spreading any more. It went secondary and once the cancer gets into your lungs, that's when there's nothing they can do. In Germany they have ways of cutting out the tumours in your lungs. They identified 42 tumours in his left lung so it was an awful operation. They cut out the tumours and then they cut out half of his left lung.

"We were waiting a few weeks to see if we could cut out the tumours in the right lung, because you couldn't do both of the lungs at the same time.

"On the day of the operation they called us in to the surgeon and he said, 'I'm terribly sorry to say but the tumours have come back into what's left of your left lung'. So, they said 'it's pointless'.

"Danny said, 'how long have I got' and they said, 'a month, six weeks'."

Danny showed incredible resilience during his ordeal.

"The thing about Danny was he never threw the head or slammed the doors and said 'why did it happen to me'," says Dave (60).

"He turned to me one day and said, 'Ah sure Dad if this has to come into our family I'm glad it was me and not you or Mum, or God forbid one of the girls'."

"As soon as he started the chemo, when he was getting sick into a bucket, I said, 'what are we going to do to take his mind off this, there's going to be months of this'. So we said, 'OK we'll get him a little dog' and we brought it into him and the little dog only fitted in your hand. The minute he saw her his eyes lit up. We said 'Danny what do you want to call her?'

"And he thought for a moment and said Chemo! I'll call her Chemo so every time I hear the word chemotherapy I will think of this beautiful little dog instead of this horrible thing I'm going through.

"Wasn't that clever of him? It worked and we still have little Chemo to this day running around the house 11 years later."