Josh Fletcher died when his car stuck a cow on the Moira Road around 3am on Sunday morning.
The 18-year-old engineering student’s car left the road following the impact and he was pronounced dead at the scene, police said.
Family friend Gaye Kerr paid tribute to the former Wallace High School pupil as the “most well-mannered and well-adjusted young man you could ever meet”.
Ms Kerr said that despite having to battle Diamond-Blackfan anemia (DBA) for most of his young life, Josh never once felt sorry for himself – and always remembered those who had helped him on his harrowing journey.
“He had to fight from the day he was born,” Ms Kerr said.
“That wee boy fought so hard to stay on this earth with his bone marrow transplant from his sister Jodie.
“For all he came through, it was never a case of ‘poor Josh’ or ‘why me?’ He just go on with it and he enjoyed life to the full.
“For him to get the gift of life only for it to be taken this way is just unbearable. He is the best wee boy I have ever met in my life and I am totally heartbroken.”
Josh had to undergo a bone marrow transplant in London, at the age of eight, in 2010. It was almost ten months later before he was well enough to come home.
Ms Kerr’s family had formed a strong bond with Josh and his family as two of her own young children were also battling serious blood disorders.
“Josh came home and did exceptionally well, only requiring yearly check-ups at the hospital. He was living life to the full,” she said.
“Josh was remarkable. He was the most well-mannered, well-adjusted young man you could ever meet. He was a credit to his mum and dad. A total credit, but most of all he was a credit to himself.”
Ms Kerr added: “He worked so hard to get where he wanted to be. He enjoyed a good laugh and a good carry on and there was never any badness in him. The memories I have of Josh are so very precious.
“Nobody knows what is around the corner. Little did I know whenever Josh was texting me on Friday that that would be the last text I would ever get from him.”
PSNI sergeant Jonny Mackenzie said Josh was travelling in the direction of Moira and was between the Moyrusk and Bushfield Road junctions when the collision occurred.
“I would ask anyone who travelled along this stretch of road in the time leading up to the collision to contact police with any information or dash-cam footage they may have. Please call on 101 quoting reference number 227 18/10/20,” he said.