{{show_title_date || "CIA director resigns, admits extra-marital affair, 11/9/12, 7:00 PM ET"}}

Reports: Petraeus had affair – and the FBI is investigating his biographer

Updated

NBC News’ chief foreign correspondent Richard Engel appeared on Hardball Friday to reveal new details surrounding CIA Director David Patraeus’ bombshell announcement that he was resigning, citing an extramarital affair.

While Petraeus’ mistress has not been officially identified, there are some clues. Engel’s law enforcement sources say the FBI is now investigating whether Paula Broadwell, Petraeus’ biographer, improperly tried to access Gen. Petraeus’ email, and that she may have accessed classified information.

Engel said the two spent extensive time together, that Broadwell has given several television interviews about Petraeus and has said the two have gone running together.

Officials said they do not believe criminal charges will be filed and that Petraeus is not under any type of investigation, Engel said.

Either way, “this is a big fall [for Petraeus]…down from where he was on our national estimate,” said Hardball host Chris Matthews. “This man was almost at the Gen. MacArthur level just a few years ago.” Petraeus’s name had been mentioned as a possible vice presidential candidate.

Engel agreed, saying it was the “fall of an American hero.”

In Petraeus’ resignation letter, he wrote, “such behavior is unacceptable, both as a husband and as the leader of an organization such as ours. He informed President Obama of his decision in a Thursday meeting.

Reports: Petraeus had affair -- and the FBI is investigating his biographer

Updated