Guy Turcotte, who was found not criminally responsible due to a mental disorder in the stabbing deaths of his two young children in 2009, is under arrest tonight after Quebec's Court of Appeal ordered that he stand trial again. 

The Sûreté​ du Québec, Quebec's provincial police force, confirmed that Turcotte turned himself in to police Wednesday evening.

He will appear Thursday in a courtroom in Saint-Jérôme, Que., which is about 40 kilometres northeast of Montreal.

Turcotte's arrest came just after the appeal court ordered a new trial in his case. A jury had previously found him not criminally responsible for stabbing his two children to death.

The court overturned that verdict Wednesday and said Turcotte should face a new trial on first-degree murder charges.

"Today, it was with satisfaction that Quebec Directors of Criminal and Penal Prosecutions received the Court of Appeal judgment of Guy Turcotte," said Crown spokesman Jean-Pascal Boucher.

Turcotte's ex-wife 'in shock'

Isabelle Gaston — Turcotte's ex-wife and the mother of Anne-Sophie, 3, and Olivier, 5 — said she welcomed the news of a new trial, but is still stunned by the Court of Appeal's ruling Wednesday.

'It’s a first step in fixing a judicial mistake that is appalling'- Isabelle Gaston, mother of Anne-Sophie and Olivier Turcotte

"I am in shock. It’s rare I‘m at a loss for words...I am frozen in my emotions," Gaston said.

"A part of me is happy — we can’t help but rejoice this news. But at the same time, a part of me is sad. I have the impression that I didn’t have to live all those uncertainties, that distress and hopelessness that I experienced with the [not-criminally-responsible] verdict on July 5. But for me, it’s a first step in fixing a judicial mistake that is appalling," she said.

Turcotte has the option of appealing to the Supreme Court of Canada, which could reinstate the jury's non-conviction verdict.

Jury found Turcotte not criminally responsible in 2011

The cardiologist from Saint-Jérôme, Que., was found not criminally responsible after he admitted to the February 2009 fatal stabbing of Anne-Sophie, 3, and Olivier, 5.

guy-turcotte-children-olivier-anne-sophie

Olivier, 5, and Anne-Sophie, 3, were stabbed to death in 2009. (CBC)

After that 2011 verdict, the Crown prosecutor sought an appeal, arguing that the judge in the first trial should have never given the jury the option of finding Turcotte not criminally responsible.

The prosecutor said there was a lack of evidence to support a defence of not criminally responsible for reason of mental illness, arguing instead that the killings were premeditated and were intended as revenge against former partner Isabelle Gaston, who was having an affair. 

Turcotte's defence lawyer had argued that his client suffered from serious mental illness during the incident, and was intoxicated on windshield washer fluid as part of a suicide attempt.

But the three judges of the province's Appeal Court found that the jury was not properly instructed about Turcotte's state of mind and the question of self-intoxication.

As a result, they concluded that the trial was skewed in favour of the accused.

Turcotte's controversial freedom

After being housed for 46 months at Montreal's Pinel Psychiatric Institute, Turcotte was released with conditions last December, despite protests from his ex-wife, Isabelle Gaston.

At the time, Gaston said she was nervous that he would come after her.

The federal government responded to the controversy, saying it would introduce legislation to make it harder for mentally ill criminals to be let out of custody.