The Ontario man accused of stalking Shania Twain shocked a courtroom on Thursday in Toronto, calling out to her while she testified via video link and announcing that he would change his plea to guilty.

Giovanni (John) Palumbo, a former Ottawa physician who has been in and out of psychiatric care since the 1990s, is accused of breaching a court order in March to stay 500 metres away from Twain, one of Canada's biggest celebrities.

But as the country-pop superstar testified via video link at Palumbo's trial at Old City Hall, she was suddenly interrupted by the accused, who rose from the prisoner's box and shouted out her real name.

"Eileen, you can trust me. I'm going to plead guilty," he blurted out.

Then he said in a quieter voice, to the judge: "I've been offended too much, your honour."

Court was adjourned shortly after the outburst, but resumed before wrapping up late in the afternoon. The trial is scheduled to resume Friday at 10 a.m. ET.

Palumbo, 51, was jailed on March 27 after he was arrested at Toronto's Air Canada Centre during an appearance by Twain at the Juno Awards. He was charged with criminal harassment and has been held in custody since.

Letters drifted into 'romantic zone'

His outburst in open court on Thursday came after nearly an hour of testimony in which Twain quoted some excerpts from love letters she said were sent to her by Palumbo in 2009.

"How about we get together a.s.a.p. so we can get to know each other in person?" one letter stated.

Another one, addressed to "Dear Eileen" and also providing his phone number, stated: "I love you more than quotes can describe. I love you more than anything in the universe. I need you more than anyone else in the world."

Twain, dressed plainly in a white cardigan with her hair in a ponytail, said she grew nervous about the letters. She said that she often received such letters from small children, but not adult men. She told the court: "I'm not responding, but he's writing as if I am."

Twain said she is normally flattered by fan mail, but that Palumbo's became more personal and disturbing, and seemed to be shifting in nature from admiration to "a romantic zone."

Twain also testified that she increased her security detail to 24 hours when she went to her cottage in Ontario's Muskoka area, knowing that Palumbo was from Ottawa. She testified that Palumbo arrived outside the gravel entranceway to her cottage in a Lamborghini, and followed her into town and also checked into a nearby resort.

Twain said Palumbo also went by her cottage in a boat more than once, showed up at her grandmother's funeral, and sent her flowers in Switzerland.

The singer said she felt that Palumbo was "maybe suicidal or in a desperate state of mind."

Twain said Palumbo showed up at the 2011 Junos, which caught her off-guard.

Home 'shrine' for singer

Twain was granted permission to testify by video rather than appear in person, after the Crown attorney made an application last month. Her location was not disclosed. 

Palumbo's ex-wife, Christel Palumbo, told Postmedia News her ex-husband had created a "shrine" for Twain in his Ottawa home following their separation, and that she discovered 30 CDs filled with images of Twain, along with videotapes documenting Twain's various televised appearances.

The material was handed over to investigators.

The defence had argued that Palumbo has never exhibited harmful or threatening behaviour, and that his actions have been merely an expression of his adoration for the superstar.