(CNN) – Former Democratic presidential candidate John Edwards has long denied that he is the father of videographer Rielle Hunter's daughter - but outspoken wife Elizabeth Edwards says she isn't sure.
In an interview with talk show host Oprah Winfrey set to air Thursday, Elizabeth Edwards says doesn't "have any idea" if her husband, who has admitted having an affair with Hunter, is also the father of Hunter's child.
"The other woman has a baby," Winfrey said during the interview.
"That's what I understand," Edwards said, interrupting the media mogul.
"And there is great speculation that your husband, John Edwards, is the father of that baby," responded Winfrey.
"That's what I understand. I've seen a picture of the baby. I have no idea. It doesn't look like my children. But, I don't have any idea," said Edwards.
In "Resilence," a new book by Edwards due out later this month, she describes her visceral, physical reaction to her husband telling her about the affair in late 2006, soon after he announced his second presidential bid.
"After I cried and screamed, I went to the bathroom and threw up," Edwards writes in her forthcoming book.
Related on TIME.com: How I survived John's affair
The Edwardses recently acknowledged a pending federal investigation into payments by the former candidate's political action committee to a production company owned by Hunter.
In a statement given to several news organizations, including to CNN on Monday, John Edwards for the first time acknowledged the ongoing federal probe, but would provide no further details.
"I am confident that no funds from my campaign were used improperly," Edwards said in the statement. "However, I know that it is the role of government to ensure that this is true. We have made available to the United States both the people and the information necessary to help get the issue resolved efficiently and in a timely manner."
Elizabeth Edwards, told CNN Monday "there won't be anything that sticks on this."
A spokesman for the U.S. Attorney's Office in North Carolina refused to confirm or deny any ongoing investigation.
It is a federal crime to knowingly use money from a political action committee for personal use.
Listen: CNN Radio reports on the Edwards investigation
Updated: 11:24 a.m.