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, in the head with an axe, then suffocated the 50-year-old man to death with a plastic bag in their family home at Greensborough in November 2020.
Heddergott thought her son, plagued by severe anxiety and depression, could not go on without her, her barrister Rishi Nathwani told the Victorian Supreme Court on Tuesday.
"She believed he did not want to continue living the life he did," Mr Nathwani said.
"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 has pleaded guilty to murder and is awaiting sentencing before Justice Lex Lasry.
"This case is in a most unusual category," Justice Lasry said.
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 used at his service 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.
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 family and friends we have left behind," Heddergott wrote.
"William loved people and wanted to connect - he hopes to be better to 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. Things just don't seem as important as they used to; I don't care about things as much anymore.
"We knew something was going on with Mum - she was acting differently. I know she's done wrong, but that's that."
Heddergott is expected to be sentenced later on Tuesday.
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