Edwards recounted the situation her book, "Resilience," and spoke about the revelation with Oprah Winfrey.
"It was...it was just a really tough. That was a really tough night," she told Winfrey.
In January, the couple separated after 30 years of marriage after John admitted he had fathered a daughter with Hunter.
Born Mary Elizabeth Anania, Elizabeth Edwards grew up in Virginia as the daughter of a navy pilot.
She initially planned to teach literature, but ultimately pursued a law degree at the university of North Carolina, where she met John.
The couple had four children.
Their oldest son, Wade, was killed in an automobile accident in 1996 at the age of 16.
"When Wade died, it was -- it was a terrible burden," she said on Larry King Live. "But it also reminded you both of the fact that you needed to grab hold of each day. You couldn't -- you couldn't just take each day for granted."
In recent years, Elizabeth authored two best-selling books and became a champion of causes involving poverty and cancer.
But always, she said, her children were her top priority: 28-year-old Cate, 12-year-old Emma Claire and 10-year-old Jack.
"It scares me the most that there's going to be a day that, you know, is likely to come before I wanted it to come where I have to tell these sweet children goodbye," she said in a Nightline interview.
In an April 2008 interview with "Good Morning America's" Robin Roberts, she said wanted her children to be able to handle any situation that comes their way.
"They have to know how to fly by themselves. They have to know what to do when the wind blows them off course. And that's what's happened to me," she said. "The wind has blown me off course, but I'm kind of thinking this might be it. That, in bad times, you still keep your eye on what it was that was important to you. And you press forward with that. And if - that's all I give them, then I would have done a really great job."
In a television appearance taped in July on the "Nate Berkus show," she talked about talking about her new furniture store in North Carolina.
"It's unlike anything I've lived before. I was sort of an at-home mother for a while, and then a political wife," she said. "So now, this is the next phase and it belongs to me. It doesn't belong to any of those things in the past."
Weeks earlier, she appeared on CNN's "Larry King Live."
"I don't think that I'm special in any way, but I think most people do pull themselves together. Do what it is they need to be done," she said. "Sometimes you're thrown for a loop for a little while and then you start to reclaim."
She told King she wanted to live eight more years to see her young children grow up.
"I'd like for them to see me seeing them off in their new life. So they -- as adults, they would see me as still, a presence in their life and not as that distant memory of the -- you know, the woman playing Legos with them on the floor, but somebody who was a real part of their lives," she said.
Sen. John Kerry, D-Mass., John Edwards' former running mate in 2004, said in a statement that he and his wife Teresa are "grateful for the time" they spent getting to know Edwards.