Police described the slaying of Connor Cleave by his knife-wielding lifelong friend Jamie Wishart as a “needless tragedy”.
Prior to sentencing Wishart on Friday to 10 years in prison for culpable homicide, Lady Scott told the High Court in Glasgow the killing was witnessed by Connor’s siblings.
She added: “He died at the scene in his mother’s arms.
“The Cleave family have been left devastated.”
The court also heard Wishart had been drinking and talking valium before the incident.
During a trial at the High Court in Edinburgh, Connor’s mother, Susan Seath (43), wept as she told the jury she arrived at the scene of the stabbing just before Connor took his final breath.
She said she saw a “big hole” in her son’s chest as he lay in the street with serious injuries.
The jury heard she ran to the crime scene in Simon Crescent after a friend told her Connor had been stabbed.
Ms Seath said: “He only took one more breath when I got there.”
She said a police office had lifted up her son’s top to see his injuries.
“He pulled up Connor’s top and you could see the big hole in his chest. That’s when he started radioing and going mental,” she said.
Another witness, Ashley Johnson (24), told the court she saw Wishart sticking “something shiny” into Connor’s body.
Defence solicitor advocate Gordon Markie said: “Mr Wishart says he intends to try and turn his life around.
“Prior to this incident, he had been drinking and taking valium. He requires to address that problem.
“He is remorseful for what he did.”
Detective Inspector Martin MacLean from Police Scotland, who led the major investigation, praised his colleagues’ professionalism and the dignity shown by Connor’s family.
“This attack, and the subsequent death of Connor, had a huge impact on the close-knit community of Methilhill in general and particularly upon the residents of Simon Crescent,” he said.
“Connor’s death was a needless tragedy, which involved two young men who had known each other for a significant part of their young lives and had grown up together.
“Jamie Wishart carried out a meaningless act of violence, which resulted in Connor sustaining a single, but fatal, stab wound to the heart. This is a telling reminder of the dangers of carrying any knife, large or small.”