According to Buzzfeed, married biographer, Paula Broadwell, accompanied the esteemed military leader on a government-funded trip to the City of Lights in July 2011 while her husband cared for their two children at home.
As the fall-out from the scandal continues, family and friends are offering support to Petraeus' wife of 38 years, Holly, who is understandably embarrassed, furious and deeply hurt.
Shocked friends said the couple appeared to have an idyllic marriage and showed "a united front" last month at their daughter's wedding, the Washington Post reported.
"When dinner was over, Holly and Dave were both beaming throughout their evening," retired Gen. Jack Keane told the newspaper.
"They made their own way around the room saying hello to their friends and relatives."
He said Holly is angry, adding "furious would be an understatement".
Petraeus's affair with Broadwell was uncovered when Broadwell allegedly sent harassing emails to Petraeus' friend, Jill Kelley, who in turn, notified the FBI.
The emails were traced to Broadwell, and further probing uncovered intimate emails with Petraeus which suggested the pair were having an extramarital affair.
Investigators said it appeared there was no compromise or breach of classified information or criminal activity.
The 60-year-old resigned to President Barack Obama Nov. 9 and issued a statement acknowledging the affair, which is believed to have begun about 16 months ago.
"After being married for over 37 years, I showed extremely poor judgment by engaging in an extramarital affair,' he said in the statement. 'Such behavior is unacceptable, both as a husband and as the leader of an organization such as ours. This afternoon, the president graciously accepted my resignation."
ABC News quoted retired U.S. Army Col. Steve Boylan, who is a former Petraeus spokesperson, who said Petraeus broke off the affair four months ago.
"He hugely regrets what happened," Boylan said.
"He pretty much threw away the best job he ever had and put his family through something just too hard to describe."
Petraeus and Holly are believed to be staying in their Arlington Home and are doing "OK."
Broadwell, 40, and her husband, Scott, and two children have also fled their home. Buzzfeed suggested the biographer has become "the Pentagon's Monica Lewinksy".
Broadwell's father, Paul Krantz, believes his daughter is the victim of "character assassination" and suggested it was a "smokescreen" and part of a cover up.
“There is a lot more that is going to come out,” Krantz the New York Daily News reported.
Russell Broadwell, Scott’s father, said he first learned of the alleged affair on the television news on Nov. 9 night.
He confirmed to the newspaper he was "astonished", and said he has since spoken to his son.
Meanwhile senior lawmakers called for an inquiry into the FBI’s handling of the case and why they were not made aware of the investigation.
The Washington Post reported Sen. Dianne Feinstein, chairman of the Senate intelligence committee, said the nation's top lawmakers were not told the inquiry was underway and only found out hours before he announced his resignation due to media inquiries.
“This is something that could have had an effect on national security,” Feinstein said.
“I think we should have been told.”
She said the panel will “absolutely” investigate why the FBI did not notify relevant officials sooner.