The Rathfarnham native (39) had a starting weight of 19st 4.5lbs. His father was diagnosed with diabetes when Killian was 15 and he died when he was 51 from a weight-related illness.
Pledging that the same thing wouldn't happen to him, the dad-of-two said he worked the hardest to get his life under control again.
"I feel a million dollars now. It's not the amount of weight that I've lost for me, it was about two main goals, to get exercise back into my life and make sure that I wasn't working myself towards and early grave."