A 51-year-old Co Kildare man has been given a life sentence for the murder of his former partner at her home in Athy two years ago.
Michael McDonald was also found guilty of assault causing harm to John Lawlor, 44, and is to be sentenced on this at a later date pending a victim impact report.
The jury returned a unanimous verdict of guilty on both counts after two hours and 41 minutes of deliberations.
McDonald did not show any reaction when the verdicts were read out.
McDonald, of Barnhill, Castledermot, had pleaded not guilty to the murder of Ms Breda Cummins on May 13, 2010 at Michael Dooley Terrace, Athy.
He had pleaded guilty on arraignment to the manslaughter of the mother-of-one but this plea was not accepted by the Director of Public Prosecutions.
McDonald further pleaded not guilty to assault causing harm to Mr Lawlor, of Pearse Terrace, Castledermot, at the same address on the same date.
McDonald, who has been diagnosed with Alcohol Dependency Syndrome and Schizoaffective Disorder by a clinical psychiatrist and had been prescribed anti-psychotic drugs at the age of 16, had previously been in a five-year relationship with Ms Cummins, who was also an alcoholic.
He had told gardaí it was a "tempestuous relationship," and that Ms Cummins started going out with Mr Lawlor several days after the break-up.
The 13-day trial heard that McDonald, who had been drinking alcohol on the evening of the murder and had taken sleeping tablets, had brought a kitchen knife from his home in Castledermot to Michael Dooley's Terrace to "rescue Breda" as he believed she wanted to return to his house.
He had phoned her 13 times that evening and called gardaí to check on her at around 11pm as he believed she was in danger.
McDonald told gardaí he thought Mr Lawlor "took advantage of her when she was vulnerable”.
McDonald arrived at the house at around midnight and asked to see Ms Cummins. Mr Lawlor and the house owner Michael Fennell were downstairs when Ms Cummins told McDonald to come upstairs; Mr Lawlor followed him to the bedroom.
A fight broke out between Mr Lawlor and McDonald and he was stabbed in the hand by McDonald with the kitchen knife.
After Mr Lawlor left the room to tend to his bleeding hand, McDonald turned to Ms Cummins and stabbed her six times in the chest with the kitchen knife and said: "I love you."
McDonald initially lied to gardaí that he did not bring a knife to the house as he thought investigators would think he went with the intention of stabbing someone. He said he had been carrying a knife around with him for a while after he claimed he was attacked in Dublin with Stanley knives several months prior to the stabbings.
McDonald told gardaí he "lost the plot" and it was not his intention to kill anyone. He said he felt betrayed that Ms Cummins had taken Mr Lawlor's side in the row.
McDonald initially told gardaí he had thought he had only stabbed Ms Cummins in the arm and had not intended to kill her but described the stabbing as a "frenzy stabbing, striking her in the heart."
Ms June Cummins, 32, a sister of Breda said, after the sentencing of McDonald, that her whole family still cannot believe Breda had died "in such a cruel way."
Ms Cummins, who was the last of her family members to see Breda the day before her death, said Breda had a "good heart" and Breda's last words to her were "I love you sis" and Breda had given her a hug.
Ms Cummins said Breda's death has affected deeply their mother Barbara, brothers John, Kenny and Jason and sisters Johanna, Sabrina and Pamela along with Breda's 15-year-old son.
The Cummins lost their sister Hazel in 2002 through natural causes. Family members wore t-shirts bearing Breda's photograph and on the back displayed Breda's birth date and death date.
"Breda's death caused us a lot of heartache and we will never forget her. Breda was a loving, caring person and had a great heart and didn't deserve what happened to her. We are delighted now we have got justice for my sister's death. She can rest in peace now with our other sister Hazel," said Ms Cummins.
Defence Counsel Feargal Kavanagh, SC, with instructing solicitor Sean Brown, in his closing speech, described the case as a "tragic case" as McDonald had been allowed to "fall through the cracks" of the health service system despite his numerous cries for help over the years.
"He was never involuntarily committed when he went for help and discharged himself several times and didn't get the treatment he required," said Mr Kavanagh.
Ms Justice Iseult O'Malley thanked the jury for their care and attention in what she said was "a sad case to listen to" and excused them from jury duty for seven years.