Giovanni (John) Palumbo is charged with three counts of failure to comply with a court order and criminal harassment by watching and besetting.
Appearing via video link in a Toronto courtroom, Twain testified that Palumbo initially made her feel uncomfortable with a series of confessional letters — but then things escalated.
"With each letter, I went from being concerned to very afraid, to be honest," said Twain, speaking from an undisclosed location in Europe.
"I started to wonder where the end to it was, and how isolated my life would have to be to avoid more contact, unwanted contact.
"I was concerned about what he was capable of."
The trial began with Twain combing over a series of letters allegedly sent by Palumbo, which included confessional statements about the author's work and home life, and sweeping declarations of love for the country star.
"Please understand that I love you more than words can describe," read one letter dated May 19, 2009.
"I love you more than anything in the universe. I need you more than anyone else in the world because I love you more than anyone else in the world could love you."
Another letter, dated Sept. 20, 2009, read: "Perhaps, because we are so perfectly matched, everyone that knows us is afraid of what would happen if we met. It is possible that there would suddenly be hell on Earth, but, it is also possible that there would suddenly be heaven on Earth."
Twain was asked again and again to characterize her response to such statements, and she repeated many of the same words: disturbed, vulnerable, unsettled, uncomfortable. She felt empathy too, but said that feeling gave way to concern as the situation intensified.
"They were uncomfortable letters, they were very personal," Twain told court. "They were more like love letters, not so much fan mail."
About one specific passage, she added: "It makes me feel uncomfortable and it makes me also feel a little bit sad and just a bit awkward."
After roughly 90 minutes of Twain's testimony, Palumbo — clad in a rumpled black suit, navy slip-on sneakers and wire frame glasses — abruptly stood and addressed the court loudly.
"Eilleen, you can trust me, I'm going to plead guilty," he said, using Twain's real first name.
"I've been offended too much, your honour."
After a short break, Palumbo remained composed as Twain testified that his worrisome behaviour extended beyond the letters.
She also told the court that she had to hire 24-hour security for an extended-family gathering at her cottage in Dwight, Ont., back in the summer of 2009, because she heard that Palumbo was planning on staying at the nearby Deerhurst Resort.
During the vacation, Twain said Palumbo was seen parked in his Lamborghini down the road, and navigating a small boat back and forth across a lake located near her cottage.
"We were trying to have a family vacation ... even though I had taken the extra measures with security, it was clear it wasn't enough," she said.
She also alleged that Palumbo had visited her brother-in-law's auto shop with a supposed car issue because he wanted to be closer to her.
"The manipulation scared me a bit," Twain said. "I was disturbed by that."
And Twain also testified that when her grandmother died in August 2009 the singer deliberated on whether or not to attend her funeral in her native Timmins, Ont., because she worried about Palumbo's presence.
"I had to think hard about whether to go to the funeral or not because I thought Mr. Palumbo would go," she said.
Twain added that she was told later that Palumbo did, in fact, attend.
Similarly, she said she fretted about attending this year's Juno Awards in Toronto, where Palumbo was arrested after allegedly trying to make contact with Twain, who was being ushered into the Canadian Music Hall of Fame.
But Twain ultimately decided to go primarily because she was thought he wouldn't be there.
"I might very well not have gone at all," said Twain, clad in a white cardigan.
To close her testimony for the day, Twain was asked by the Crown whether she ever wanted to have contact with Palumbo in any capacity again.
"No, I'm afraid not," she replied.
The trial continues Friday and is scheduled to last three days.