A pensioner killed his childhood friend after "harmless banter" about when they were youngsters.
John Green, 67, punched John Thomson, who fell and suffered a fatal head injury following the attack in Lanark.
The 69 year-old dad passed away two years after he had lost his wife in a car accident.
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First offender Green now faces a jail-term following his guilty plea to the culpable homicide of Mr Thomson.
Prosecutor Erin Campbell told the High Court in Glasgow how the men had been friends since childhood.
On the afternoon of the killing last July 9, they had their regular Saturday meet-up at Lanark Bowling Club in the town's Waterloo Road.
They were joined by other friends Jim Stewart and Tom Neil.
The group were described as in "good spirits" with no animosity between them.
Green's son-in-law John Gardiner later picked the men up that night to take them home.
Mr Neil was dropped off first before they headed to Mr Thomson's.
Miss Campbell said: "While en-route, Mr Thomson engaged in what was described as harmless banter with Green.
"He was saying things along the lines of: 'Remember when we were boys, Kirkfieldbank used to beat the boys from Crossford'.
"Mr Thomson was originally from Kirkfieldbank and Green from Crossford.
"Green took offence to these comments."
The car then stopped near Mr Thomson's home in the town's Kenilworth Road and the OAP got out.
Raging Green -who latterly worked for an interior firm - then stormed after him and confronted his friend.
Mr Thomson said: "What you doing, John? Get back in the motor."
Miss Campbell: "Green and Mr Thomson then exchanged words. Green proceeded to punch him to the right hand side of his face twice in quick succession.
"Mr Thomson fell to the ground and hit the rear of his head off the pavement."
The other men got out to help and found the stricken victim lying unconscious.
There was blood on the pavement and he had a large gash to his head.
Green, also of Lanark, was standing against a wall and was heard stating: "I am sorry, I am sorry."
Mercy crews soon arrived at the scene to try and help Mr Thomson.
It was there Green further stated: "I am guilty. He slapped me 40 years ago, so I slapped him back tonight, but he is my mate."
After initially being arrested for assault, he added: "Honestly, it is something that should not have happened."
Mr Thomson was rushed to hospital and was found to have a significant head injury. He never recovered and died three days later.
He also had a bruise at his jaw as a result of a punch of "low level force".
The court heard Mr Thomson is survived by two adult sons. His wife - who was not named during the hearing - was killed in a road traffic collision in March 2020.
Green's lawyer Edith Forrest told the court he had been left troubled by what happened.
The advocate: "He is really unable to put into words how desperately sorry he is for what he done.
"He wishes to convey his apologies to Mr Thomson's family.
"This is a most unusual and very tragic case, but one that he appreciates the severity of."
Lord Richardson agreed to continue bail for Green as sentencing was deferred for reports until May 17 in Edinburgh.
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