ABC News first learned the pair are legally separated from a source close to Elizabeth Edwards. Under North Carolina law, couples can't get a divorce until they've been legally separated for at least a year.
The news came the same day that excerpts from a new book by former Edwards aide Andrew Young were published by the Wall Street Journal.
Young writes the two-time presidential candidate told him he thought about leaving his wife but also cited his love for her as a reason to keep details of an affair hidden.
The Journal reported on its Web site that Andrew Young says Edwards asked him to go into hiding with Edwards' mistress, in part because of his wife's health.
Young wrote that Edwards concluded "that if I helped him, I would make Mrs. Edwards's dying days a bit easier. 'I know you're mad at her, Andrew, but I love her. I can't let her die knowing this."' Elizabeth Edwards has an incurable form of cancer that returned in 2007.
Young's tell-all book accounts how Edwards asked him to help cover up the affair and promised to take care of him in the future. Edwards acknowledged for the first time last week that he fathered a child with Rielle Hunter.
The book, "The Politician," is not due out until Saturday, but the Journal said it purchased a copy Monday at a Washington-area book store.
Young provides an unflattering portrait of Edwards, talking about his obsession with campaign donations, his fixation with his hair, his disapproval of "fat rednecks" at state fairs and the lengths he went to hide the affair. Young has said in excerpts of an ABC News interview that Edwards asked him to find a doctor to fake a paternity test and to steal a diaper from the baby to secretly do a DNA test.
A longtime aide to Edwards, Young describes the discovery of a videotape showing Edwards and a naked Hunter.
"It was like watching a traffic pileup occur in slow motion -- it was repelling but also transfixing," he writes, according to the Journal.
Through her publisher, Elizabeth Edwards did not comment on the seperation report, but did address two allegations in Young's book: That Edwards sought to capitalize on her cancer and that she knew about the paternity of Hunter's child early on.
"Elizabeth is moving on with her life and wants to put this difficult chapter behind her. It was an excruciatingly painful period for her and she no interest in rehashing the past. Based on the limited portions of the book that have been made available, it is clear it contains many falsehoods and exaggerations. She will not engage in a dialogue on each of the false charges, but would like to set the record straight on two key points. First, the allegation that she sought to politicize her cancer is unconscionable, hurtful and patently false. Second, she believed Andrew Young to be the father of this child until her husband confessed his paternity to her this past summer. She will have nothing further to say."
Husband John, a former North Carolina senator and 2004 Democratic vice presidential candidate, has largely stayed secluded since first admitting the affair in August 2008. He has acknowledged a federal investigation into his campaign finances.
Edwards spent part of last week in Haiti helping with relief efforts.
In a statement to the Associated Press Wednesday, Edwards said he still cares deeply about his wife despite the couple's separation.
"It is an extraordinarily sad moment, but I love my children more than anything and still care deeply about Elizabeth," he said.