The estranged husband of a mushroom cook accused of murdering his parents and aunt will return to the stand in her trial.

Mother-of-two Erin Patterson is facing trial in the small regional town of Morwell, about 150km from Melbourne, after pleading not guilty to three counts of murder and one of attempted murder.

She admits to serving a beef Wellington to four of her former in-laws but claims she did not know it was poisoned with death cap mushrooms.

Patterson has pleaded not guilty to three counts of murder over the deaths of her husband Simon’s mother and father, Don and Gail Patterson, and his aunt Heather Wilkinson, who all attended a lunch at her regional Victorian home on July 29, 2023.

She has also pleaded not guilty to the attempted murder of Mr Patterson’s uncle Ian Wilkinson, the only surviving guest from the poisonous lunch.

Her defence said what happened was “a tragedy and a terrible accident”.

Mr Patterson, who declined an invitation to attend the lunch, gave evidence to a jury of 15 last week and his cross-examination by defence barrister Colin Mandy SC will continue today.

He detailed his “up and down” relationship with Patterson over the years since they married in the mid-2000s before separating on friendly terms in 2015.

But he said their relationship began to deteriorate in late 2022 after Patterson requested her husband start paying child support.

He decided to involve a mediator to sort it out as Patterson became “extremely aggressive” in the group chat with his parents, he told the jury on Friday.

In his earlier evidence, Mr Patterson broke down as he described seeing his mother and father inside a hospital after Patterson fed them a poisoned beef Wellington at her home in July 2023.

“Dad was substantially worse than mum. He was really struggling,” he said, before crying in court.

“He wasn’t right inside. He was feeling pain.”

Mr Patterson told the court he thought it intriguing the accused had not sought details about the condition of his parents.

The jury will return to Latrobe Valley court house about 10.30am on Monday.