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The widening scandal surrounding David Petraeus' affair has come to center not only on his mistress, but another woman whose relationship with the key players has raised tantalizing questions.

Jill Kelley is a well-connected socialite who lives with her surgeon husband in a Tampa mansion where they entertain the military's top brass. The 37-year-old mother of three is also a close family friend of Petraeus, 60, and according to sources regularly went shopping with the retired general's wife of 37 years, Holly.

Practically every recent development in the case seems to somehow involve Kelley.

Emails sent from Petraeus' biographer, Paula Broadwell, to Kelley ultimately led to the FBI's discovery that Broadwell and Petraeus were having an affair. Further, the FBI agent Kelley originally alerted about the emails was later taken off the case after concerns about his conduct, Fox News has learned -- including accusations that he sent shirtless photos of himself to Kelley.

But in the latest revelations, federal authorities are now reviewing between 20,000 and 30,000 pages of "potentially inappropriate" emails and other communications between Kelley and Gen. John Allen, the top U.S. commander in Afghanistan.

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The nature of those emails is unclear. A senior defense official said that some of the documents and emails, many of which are emails sent from 2010 through 2012, were "flirtatious." Fox News was also told that the number of actual emails was only in the hundreds -- friends of Kelley say they were harmless and might have included the word "sweetheart" here and there.

However, two U.S. officials tell Fox News that Allen's contact with Kelley was more than just general flirting. One official described some of the emails as sexually explicit and the “equivalent of phone sex over email.”

The emails would have spanned Allen's time as the deputy commander of Central Command in Tampa and his tenure as commander in Afghanistan, which began in July 2011. Allen's nomination to become the next commander of U.S. European Command and the commander of NATO forces in Europe has since been put on hold. Allen, who is married and was in Washington this week for his now-delayed nomination hearing, denies wrongdoing.

Kelley, meanwhile, has hired high-profile attorney Abbe Lowell, who previously represented disgraced Democratic presidential nominee John Edwards. Calls seeking comment from Lowell on Tuesday were not returned.

Sources close to the family told Fox News that Kelley, an unpaid social liaison to the military's Joint Special Operations Command in Florida, was not having an affair with Petraeus.

Still, it appears Broadwell suspected something was going on behind the scenes. In one of the anonymous emails allegedly sent by Broadwell to an account shared by Kelley and her husband, she claimed to have seen Kelley touching "him" -- an apparent reference to Petraeus -- provocatively underneath a table.

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Kelley comes from a Lebanese family that emigrated to Philadelphia in the mid-1970s, and she later moved to Tampa around 2002 with her husband. The Kelleys frequently hosted gatherings for military personnel at MacDill Air Force Base in Tampa, home of U.S. Central Command.

Shortly after moving to the area, the Kelleys' $1.5 million, nearly 5,000-square-foot mansion became the "place to be seen" for military personnel. Petraeus himself marked his first celebration of the city's annual Gasparilla Pirate Festival on the Kelleys' lawn, the Tampa Bay Times reports.

Linda Baldwin, the owner of a company that catered that party, told the newspaper that Jill Kelley was an "awesome" client.

"Did so much for the military, fabulous mother and amazing wife; can't say enough nice things about her," Baldwin told the newspaper. "She never spared anything for the military. It was all about them."

Just three months after posing with David and Holly Petraeus on their lawn in 2010, the Kelleys were served with a foreclosure lawsuit. The suit focused on an office building in downtown Tampa, where court records indicated they owed the bank nearly $2.2 million. In 2011, a judge ordered the property to be put up for sale, the Tampa Bay Times reports.

Friends of the Kelleys told the newspaper that Jill Kelley's favorite topic of conversation is her husband, whom she sometimes refers to as "Dr. Kelley." Scott Kelley, a celebrated surgeon who previously worked at the Moffitt Cancer Center in Tampa, is one of the world's few doctors who specialize in a type of surgery to cure cancer of the esophagus.

Since the Kelleys have arrived in Tampa, however, one or both have been the subjects of lawsuits a total of nine times, including an $11,000 judgment against them that originated in Pennsylvania. Other ongoing cases include, according to the newspaper and court records, an indebtedness case from Chase Bank, a foreclosure case from Regions Bank and a credit card case from FIA Card Services.

In another twist, court records and sources close to the Kelley family indicate that Petraeus and Allen intervened last September in a custody dispute on behalf of Jill Kelley's twin sister, Natalie Khawam. Both men wrote letters supporting Khawam, who met Allen when he was deputy commander of U.S. Central Command in Tampa, where they attended social functions.

The Associated Press contributed to this report.