And the scandal's become so complicated you need a scorecard to keep track:
A highly decorated four-star Army general lauded for his leadership of the Iraq and Afghanistan wars, Petraeus, 60, moved into the civilian world to become CIA director in September 2011. He shocked official Washington on Friday by admitting an extramarital affair with his biographer and resigning his spymaster post.
The other woman. Now a 40-year-old author and married mom of two young children, she was a West Point-educated Army reservist and graduate student when she met Petraeus at Harvard in 2006. She later embarked on a case study on his leadership of the Iraq War. After he took the helm in Afghanistan, Broadwell expanded her work into a biography, gaining unprecedented access to Petraeus and his commanders. It's called "All In: The Education of General David Petraeus."
Their affair began in November 2011, a couple of months after he became CIA director, according to retired Army Col. Steve Boylan, a friend of the Petraeus family. It ended last summer, Boylan said.
The relationship was exposed after Broadwell of Charlotte, N.C., sent emails to another woman, Jill Kelley, warning her to stay away from Petraeus, officials said.
All threads in the story trace back to this Tampa, Fla., socialite.
A surgeon's wife and mother of three children, Kelley is a sort of self-appointed social ambassador for the nearby U.S. Central Command and other officers at MacDill Air Force Base. The Kelleys opened their bayside home to lavish parties where military brass mingled with Tampa's elite. In this role, she befriended Petraeus and his wife, Holly, when he took over Central Command in October 2008.
Kelley, 37, stayed in close contact with Petraeus after he left to take command of the Afghanistan war. They exchanged nearly daily emails in an account routinely monitored by his aides, according to two former staffers, who said those messages weren't romantic in tone.
In May, Kelley started getting anonymous, harassing emails warning her away from Petraeus. She reported the email to the FBI.
The FBI traced the messages to Broadwell, uncovering her affair with Petraeus. The FBI notified Petraeus' boss, Director of National Intelligence James Clapper, who urged him to resign.
And the FBI found something more.
It unearthed "inappropriate communications" between Kelley and another top military officer, John Allen, according to Pentagon officials.
The four-star Marine general who followed in Petraeus' footsteps at Central Command and then as top U.S. commander in Afghanistan is now following him into choppy waters.
The Pentagon is investigating 20,000 pages of documents and emails involving Allen, who is married, and Kelley. Some of the communications were "flirtatious," according to a senior defense official, who spoke on condition of anonymity because he wasn't authorized to discuss the case publicly.
Like Petraeus, Allen, 58, was part of the Tampa social circle; he moved up to acting commander when Petraeus left for Afghanistan. When Petraeus came home from Afghanistan, Allen moved into the top job there—his current post.
President Barack Obama has nominated Allen to take over U.S. European Command and lead all NATO forces in Europe. That's been put on hold. He denies any wrongdoing and remains in charge in Afghanistan.
Kelley's twin sister also socialized with the two generals. Both Petraeus and Allen wrote letters lauding Khawam as a devoted mother to help her in a bitter child custody battle with her ex-husband. Earlier in that divorce case, Superior Court Judge Neal Kravitz had criticized Khawam for a lack of honesty and "misrepresentations about virtually everything."
Petraeus' wife of 38 years, mother of their two grown children, is in charge of service member assistance at the Consumer Financial Protection Bureau and is a well-known advocate for military families. Mrs. Petraeus is said to be devastated by her husband's infidelity. "Furious would be an understatement," family friend Boylan told ABC's "Good Morning America."
THE SHIRTLESS FBI AGENT
And then there's this unnamed character: The FBI agent to whom Kelley first took her complaint was a longtime friend. And he had once sent her shirtless photos of himself, according to a federal law enforcement official.
He passed the information along to others for investigation, and was subsequently told to steer clear of the case because his superiors worried that he had become obsessed with it, the official said.
But the agent passed along a tip about Petraeus' affair to Republican Rep. Dave Reichert of Washington state, who got word to House Majority Leader Eric Cantor on Oct. 27, nearly two weeks before the scandal became public.
Associated Press writers Robert Burns, Pete Yost, Kimberly Dozier, Pauline Jelinek, Lolita Baldor, Adam Goldman and Jack Gillum contributed to this report.
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