When Erica Heddergott came to the belief she was dying of brain cancer, the 82-year-old woman took action.
She struck her son William twice in the head with an axe, then suffocated the 50-year-old to death with a plastic bag in their Greensborough family home in November 2020.
Heddergott, who pleaded guilty to murder, on Tuesday faced the Victorian Supreme Court and was sentenced to 15 years in prison.
The elderly woman thought her son, plagued by severe anxiety and depression, could not go on without her, defence barrister Rishi Nathwani said.
"She believed he did not want to continue living the life he did," Mr Nathwani told the court before his client was sentenced.
"Rather than putting the burden on anyone else, she made the decision to kill him and then kill herself. That is not an excuse ... but that appears to be her rationale.
"She elected to effectively euthanise her son."
Heddergott was diagnosed with meningioma, a tumour that begins in the brain or spinal cord.
Medical evidence indicated it was benign, but the 82-year-old woman came to believe she was dying of brain cancer.
Heddergott pre-arranged funerals for her and her son before the murder.
She changed the photo to be placed on his coffin about two weeks before his death and also tried to withdraw funds from his superannuation account.
A Meals on Wheels worker found William Heddergott lying on a couch with a plastic bag firmly tied over his head.
His body was "stiff and cold", the woman said, while an examination revealed he had a blood-alcohol reading of more than three times the legal driving limit.
Erica Heddergott was discovered on the floor next to a Jim Beam bottle after trying to take her own life. She was taken to hospital and made a full recovery.
She had also left behind a farewell note.
"Time has run out and I apologise for all the loose ends and work I left, " Heddergott wrote.
"William loved people and wanted to connect - he hopes to be better next time."
The 50-year-old had moved back into the family home to live with his mother after spending two years in residential care.
Staff at the home described Mr Heddergott as a gentle and caring man.
His brother said he was a good guy who had a "big heart".
"I try and be brave but it's killed me," Andrew Heddergott said in a statement read out in court on Tuesday.
"I don't feel like going to work ... I don't care about things as much anymore. We knew something was going on with Mum - she was acting differently."
Heddergott was a "highly controlling" woman who limited her son's social interactions and ensured he became dependent on her from a young age, prosecutor Patrick Bourke QC said.
Justice Lex Lasry said that while the 82-year-old woman had lived a good life until the murder of her son, she would now likely die in prison.
"Whatever your motivation - it must have involved a high level of violence with a weapon," Justice Lasry said.
"William was vulnerable due to his mental health problems and his reliance on you. Your actions have diminished an otherwise long and law-abiding family life."
Heddergott must serve at least 10 years behind bars before being eligible for parole.
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Australian Associated Press