Retired Quebec judge Jacques Delisle was found guilty Thursday of murdering his disabled wife, as his family members' screams and sobs filled the courtroom.

Delisle, 77, is believed to be the first Canadian judge to stand trial for murder. He will automatically receive a life sentence with no chance of parole for 25 years.

Delisle's wife, 71-year-old Marie-Nicole Rainville, was found dead in the couple's Quebec City condo on Nov. 12, 2009, with a .22-calibre pistol at her side.

Delisle called 911 and told the operator his wife committed suicide by shooting herself in the head. He maintained that Rainville, who had suffered a stroke two years earlier and was paralyzed on her right side, was already dead when he arrived home.

But at trial, prosecutors argued that Delisle killed his wife because he wanted to start a new life with his former secretary and mistress, Johanne Plamondon, and avoid a potentially messy and costly divorce.

When the guilty verdict was announced in court Thursday, Delisle's family "just erupted into sobs," CTV Montreal's Maya Johnson reported.

Delisle's son was so emotional that security guards had to escort him out of the courtroom, Johnson said. He had started to behave erratically, taking off items of clothing and cursing.

"He wanted to give his father a hug. He said he wanted just one chance to be close to his father before he went off to jail and he was not allowed to approach his father," she said.

"He was quite upset by this."

Johnson noted that the verdict, reached after the jury deliberated for three days, seemed to take a lot of people in the courtroom by surprise.

Prosecutor Steve Magnan said it's the verdict the Crown had expected.

"We believe in our case and we are proud of the verdict," he told reporters outside court.

Delisle's defence lawyer, Jacques Larochelle, did not speak to media Thursday.

While Delisle often wept during testimony at his trial when his wife's physical challenges and deteriorating health were discussed, he never took the stand in his defence.

Plamondon, the woman he had been having an affair with, testified she was ready to move in with Delisle a few days before he was arrested for Rainville's murder in 2010.

Plamondon, 57, had started working for Delisle as a legal secretary in 1983 when he was named to Quebec Superior Court. She followed him when he was appointed to the Quebec Court of Appeal in 1992.

Plamondon testified that she and Delisle were just friends for years, but their relationship evolved in the months before Rainville's stroke in April 2007.

Shortly before she died, Rainville also underwent surgery for a hip fracture. She feared being a burden on her family and had wanted to go to a nursing home, instead of returning to the condo, Rainville's sister testified at trial.

Police initially believed Rainville's death was a suicide, but further investigation led to a first-degree murder charge against her husband.

With a report from CTV Montreal's Maya Johnson and files from The Canadian Press