Petraeus' affair began after he left Army

David Petraeus' extramarital affair with his biographer started after the retired general left the army, according to retired Army colonel Steve Boylan.

Boylan, who served as Petraeus' spokesman in Iraq and remains friends with him, said in an interview on Good Morning America on Monday that Petraeus and Paula Broadwell's affair started about two months after he took over as director at the CIA in September 2011. The affair ended about four months ago, Boylan said.

Petraeus, 60, perhaps the most heralded military officer of a generation, abruptly resigned from his CIA post on Friday, acknowledging that he been involved in an extramarital affair.

There are still many unanswered questions about the affair that led to Petraeus' ouster from the agency. But it's clear that the FBI had become aware of the relationship during the course of an unrelated security investigation.

On Sunday it was revealed that the FBI investigated a series of allegedly harassing e-mails to a Tampa woman named Jill Kelley that they determined were from Broadwell. A spokeswoman for Kelley issued a statement on Sunday saying that Kelley and her family have been friends with Petraeus and his family for more than five years.

Broadwell traveled to Afghanistan in 2010, while Petraeus was still serving there as the top commander. He reportedly granted her wide access as she reported on a glowing biography, All In: The Education of General David Petraeus. Broadwell has said that she first met Petraeus in 2006, while she was a graduate student at Harvard University.

"He deeply regrets and knows how much pain this causes his family," said Boylan, adding that Petraeus' wife, Holly, "is not exactly pleased right now."