An estranged husband stabbed a man who had returned home with his wife.
William Stupart lunged at Roy Clark and a struggle broke out with both men ending up on the floor.
Stupart, 31, knifed his victim in the chest before fleeing from the scene, the High Court in Edinburgh heard.
Mr Clark was taken by ambulance to Dundee's Ninewells Hospital where he was found to have suffered a collapsed lung following the attack and a chest drain was inserted.
Stupart, a council refuse collector, admitted assaulting Mr Clark to his severe injury and to the danger of his life on March 4 this year by striking him with a knife at Wolseley Street, in Dundee.
Advocate depute John Scullion said at the time of the offence Stupart was married to Fiona Souttar but the couple were living apart.
He said: "The marital relationship had broken down irretrievably according to Ms Souttar due to a number of domestic incidents which resulted in the accused being prosecuted.”
Stupart had been freed on bail about a month earlier at Dundee Sheriff Court following an assault and special conditions were imposed on him designed to prevent him having contact with his wife.
But in the early hours of March 4 Ms Souttar returned home with two friends, Mr Clark and Hazel Wilson, and noticed the rear door of the close was open.
As she went into her flat she saw Stupart at the living room door and realised that he was holding a knife.
Mr Scullion said: "Fearing for her safety she ran past her friends out into the street."
She went to get a neighbour's help to call the police. The prosecutor said Stupart walked towards the friends and was heard to say to Mr Clark: "Who the hell are you?""
At this point the accused seemed to focus his attention on Mr Clark and he made a lunging motion towards him," said Mr Scullion.
The attack victim tried to move out of the way but ended up in a struggle with Stupart.
"Both ended up on the ground, Roy Clark on his back and the accused astride him at which juncture the accused stabbed the victim in the chest with the knife he was holding," said Mr Scullion.
Defence counsel Susan Duff said Stupart, described as a prisoner in Perth, put forward no excuse for his behaviour and added: "He regrets his behaviour."
She said she was not seeking bail for Stupart who realised he was facing a custodial sentence.
The judge, Lady Stacey, deferred sentence for the preparation of a background report and remanded him in custody.
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