A teenager who stabbed his mother's ex-boyfriend to death during a domestic row was trying to protect "the most important person in his life", a barrister has told the Central Criminal Court.
Michael Bowman SC said his client, Alexander Whelan, "sprang to his mother's defence", having previously seen the deceased, Bruno Rolandi, assault his mother.
He made a "split-second decision" which counsel said has had tragic consequences for him and the Rolandi family.
The court heard Mr Rolandi was a violent heroin user.
Alexander Whelan (19) had originally been charged with murdering Mr Rolandi (56) at Green Road, Ballymoran, Edenderry, Co Offaly, on November 19, 2017.
Mr Whelan, with an address at Green Road, Lumville, Edenderry, pleaded guilty when a charge of manslaughter was put to him at the Central Criminal Court in November last year.
Detective Sergeant Caroline Lyng told the court that Alexander lived with his mother, Mary, and his older brother, Victor.
His father died when he was two years old and his mother developed an "on and off" relationship with Mr Rolandi.
There was "tension" in the house, she said, and the two brothers put this down to Mr Rolandi being there.
On the night in question, Mr Rolandi became "petulant" during a row over a wi-fi password and the accused, who was then aged 17, saw Mr Rolandi "pawing" at his mother's breasts. He became upset and called his brother Victor on the phone.
The two boys and their mother went to the kitchen and talked about telling Mr Rolandi he should no longer live with them. But he came into the kitchen and there was a "kerfuffle" between Victor and the dead man.
Mr Rolandi tried to grab Ms Whelan, so Victor stood in front of his mother and pushed Mr Rolandi.
There was "a lot of pushing and shoving and shouting" before Mr Rolandi got hold of Victor with one hand and raised the other fist "as if he was going to strike".
Ms Whelan tried to put herself between the two men and then Alexander "decided to act". He took the knife from a cupboard in the kitchen and stabbed Mr Rolandi three times.
The family immediately alerted the emergency services and Alexander "put his hands up".
Det Sgt Lyng agreed there was no attempt to clean the weapon or engage in any kind of cover-up. Alexander and his family cooperated fully with gardaí.
She also agreed that Alexander was "the last person in the world you would expect to find in this situation".
He pleaded guilty to manslaughter at the earliest opportunity and has no previous convictions, nor has he previously come to the attention of gardaí.
Despite being charged with the offence he "struggled on" to complete his Leaving Cert and has since started working.
Det Sgt Lyng agreed with Mr Bowman that Victor called 999 that night immediately after the stabbing. When emergency services arrived they found Alexander "in a panic" trying to stop the bleeding in a bid to "undo the damage".
She agreed when Mr Bowman said: "He was in a state of shock, panic, shaking like a leaf." At one point he was seen on his hands and knees uncontrollably sobbing.
Another witness at the scene said he overheard the boy's mother apologising for "putting him through this".
Alexander replied: "This is not your fault. Please don't blame yourself. Promise me you won't blame yourself."
Det Gda Lyng agreed the deceased weighed more than 16 and a half stone and was more than 6ft tall. Alexander was 5ft 7in at the time and "of a slight build and physically immature for a boy his age".
The court heard there had been violent episodes, in particular during family holidays to Turkey in 2013 and 2017, during which the two brothers witnessed Mr Rolandi assaulting their mother.
Mr Bowman handed a number of testimonials to Mr Justice Michael White, including one from his school headmaster who said that in 34 years he "can't think of a student with a better temperament".
He also pointed to psychological and probation reports which stated that Mr Whelan is "not quick to anger" and does not act in temper.
A number of witnesses had described his mother as "the most important person in his life", and Mr Bowman said he felt "overwhelmed and sprang to his mother's defence".
In victim impact statements, the deceased man's family said they "strongly disagree" with the description of Mr Rolandi, who they said was a "kind man" and a good father.
Sentencing will take place on March 2.