NAPANEE, Ont. - David Frost engaged in threesomes with two teenage hockey players he was coaching and their girlfriends in the 1990s, the sexual exploitation trial of the former NHL agent heard Monday.

One of the women, now 28, detailed for the court how, during the first of two threesomes, her boyfriend had sex with her first while Frost was lying underneath her, asking her how she liked it.

Her boyfriend then helped her on top of Frost so she could have sex with him, court heard.

"I didn't really know a lot about sex," the woman, who was 16 at the time, testified Monday, adding she lost her virginity to the boyfriend.

"I didn't even know at first what was happening."

Frost, 41, has pleaded not guilty to four counts of sexual exploitation against two former junior A Quinte Hawks players who cannot be named.

The Canadian Press is also not identifying the woman who was testifying Monday about having sex with a player during the period of the alleged offences, when she was a juvenile, though she is not part of the same publication ban.

Court heard Monday that the girl and her friend both had threesomes with their boyfriends and Frost in 1997.

The woman, who was visibly upset during her testimony, told the court her boyfriend persuaded her to engage in the alleged sex acts.

On cross examination, she said she wanted to fit in with her best friend -- who she said had already had a threesome with her boyfriend and Frost -- and that was also part of the reason she was persuaded.

In her diary, she had made a list of pros and cons about having a threesome, court heard.

The pros were "fun, experience, he wants me to."

The cons were "uncomfortable" and "increased chance of pregnancy."

The diary was a point of contention for Frost's defence team. Defence lawyer Marie Henein charged that the woman brought it forward after charges against Frost relating to her and her friend were withdrawn.

Most of the alleged incidents the woman described took place in a hotel.

When Frost joined the Quinte Hawks he brought players with him, who witnesses have testified were a tight group, isolated from the rest of the team, and allegedly under Frost's complete control. Frost and some of his players were living at the hotel.

The woman's boyfriend was billeting with a family.

The woman testified that she and her friend, who was also dating a player, would often go to the hotel to visit and "had a lot of sex."

One time, she told the court, she and her boyfriend tried a new position and afterward Frost came into the bedroom and asked the boy if he had done the positions. The boyfriend replied they had done one, and Frost offered to come in and help with the other position, she said.

"I didn't want him to," she said. "I was, I guess, shocked."

Crown attorney Sandy Tse asked the woman to confirm she had consented to the sex and she agreed.

"I was uncomfortable with it, but... I felt kind of pressured to do it," the woman said.

The woman told court her boyfriend kept asking her to have another threesome, for his birthday.

"I didn't want to do it again, but finally I got persuaded into it," she said.

"It was... more or less them," taking turns, she testified.

She knew the date was March 24, 1997, because of what she had written in her diary, where she counted how many times she had sex with her boyfriend, she testified.

"I listed it in the back of my book," she said.

"I put six times minus two...Whenever I had sex with Dave I didn't want to count him."

The young couple broke up a couple of months later.

The defence disputed the woman's version of events, pointing to both her diary and an email from her best friend to refute the woman's claims.

Henein suggested the email, sent some 18 months after the alleged threesomes, was evidence those incidents never happened and contradicted their story.

"When the email gets produced (for the case) and puts the lie to the story that you have told," that's when the diary detailing the alleged threesomes appeared, she said.

The woman said she didn't bring her diary forward during her first contacts with police because she was embarrassed about its contents, but Henein noted that after the diary was produced the woman told police: "I thought we had enough."

The trial continues Tuesday.