Guy Turcotte's ex-wife says she never believed he could have killed their kids

Isabelle Gaston, centre, ex-wife of Guy Turcotte, arrives to testify at the courthouse, Monday, September 28, 2015 in Saint-Jerome, Que. Turcotte is being retried for the murder of his two children. (THE CANADIAN PRESS/Ryan Remiorz)

SAINT-JEROME, Que. -- The ex-wife of a former Quebec doctor who is charged with murdering their children says she never thought he could kill them.

Isabelle Gaston was back on the stand Tuesday at Guy Turcotte's first-degree murder trial.

Turcotte faces two counts of first-degree murder in the 2009 slayings of Olivier, 5, and Anne-Sophie, 3.

"I never thought he could kill them," she repeated more than once during her testimony Tuesday.

Turcotte, 43, has pleaded not guilty to the charges but admitted through his lawyers last week to causing the children's deaths.

Under cross-examination by Turcotte's lawyer, Guy Poupart, Gaston was asked at length about her relationship with the accused in 2008, leading up to the deaths in February 2009.

"It was a difficult year," she said. As the couple drifted further part, there were numerous skirmishes, harsh words and strife.

Gaston told Poupart there was no physical violence, but that in retrospect she now considers herself a victim of domestic violence because of the emotional abuse from her former spouse.

"He did not hit me, but there was verbal and psychological violence," Gaston said, describing what she called incessant denigration by Turcotte.

Questioned by Poupart, Gaston said she could be sharp-tongued, too.

"I was also verbally abusive," she said. "It was like a spiral."

"We had a toxic dynamic," Gaston added.

She began seeing her personal trainer and she and Turcotte split up in January 2009 -- less than one month before the children were found dead in a rental home.

The court heard the new beau, Martin Huot, became a regular presence at the former family home as soon as Turcotte left.

Gaston said the reason for Huot's presence was twofold: she no longer wanted to be controlled and she feared for her safety with regard to her ex-husband.

A date had been set for the couple to meet with a mediator to discuss custody matters.

"We never met, the children were dead," said Gaston, who left the courthouse without comment.

The trial continues Wednesday.