Valerie Vetrano, an openly gay sales rep from Corona, Calif., claims she had a lesbian relationship with Prejean's mom, Francine Coppola.
"I did date her," she told ABCNews.com Wednesday evening. "I'm not going to deny it, but I'm not going to say anything else."
Vetrano, whose connection to Coppola was first reported by Star magazine, declined to comment on how long their relationship lasted but confirmed it ended "a couple weeks before Carrie Prejean was in the Miss USA competition."
According to an unnamed friend quoted by Star, Coppola's family knew nothing of her affair, although during her 1996 divorce from the beauty queen's father, Wil Prejean, both parties made gay allegations against the other.
ABCNews.com's attempts to reach Coppola and Vetrano for comment were unsuccessful Wednesday evening. Prejean declined to comment through her representatives.
Prejean ignited a fire storm of scrutiny following the 2009 Miss USA pageant in April.
When asked whether she supported same-sex marriage by pageant judge Perez Hilton, Prejean replied, "I think it's great that Americans are able to choose one or the other. We live in a land where you can choose same-sex marriage or opposite marriage. And you know what? I think in my country, in my family, I think that I believe that a marriage should be between a man and a woman. No offense to anybody out there, but that's how I was raised."
While Hilton and others condemned her handling of the question, the 22-year-old beauty queen defended herself via multiple media outlets and church guest stints. Though she appeared in a PSA for the National Organization for Marriage, which campaigns against the legalization of same-sex unions, Prejean insisted she wasn't close-minded. She told "Access Hollywood" that her sister is a gay activist.
"My sister is a second lieutenant in the Air Force and she is a gay rights activist," Prejean said, adding that her sister is not gay. "She supports gay people, she supports gay marriage. My beliefs have nothing to do with my sister or my mom, or whatever."
Shortly after, Prejean's sister Christina told ABCNews.com she was surprised the beauty queen called her a gay activist.
"I have never even given myself that title. I was kind of surprised that she mentioned it, but I think she wanted to get the point across that our family is tolerant," Christina Prejean said, adding that she only recently got involved in gay rights activism.
Earlier this month, when Prejean's title as Miss California USA was called into question because of her alliance with the National Organization for Marriage and a series of semi-nude photos that emerged on the Internet, Coppola said her daughter was being "persecuted" for her views.
"She was raised in a Christian home. Marriage is between a man and a woman. Now she's being persecuted for speaking her opinion," Coppola told the blog MomLogic.com. "As a mother ... I'm proud of her, that I raised a daughter that has morals, values, and integrity to speak the truth."