John Allen biography: general is married to Kathy Allen and has two daughters, Bobbie and Betty

General John R. Allen is the second top military official dragged into the David Petraeus sex scandal after being accused of sending thousands of “inappropriate” emails to socialite Jill Kelley, the woman responsible for exposing the former CIA director’s extra-marital affair.

General John R. Allen, commander of U.S. and NATO troops in Afghanistan, is under investigation by the FBI after the agency discovered between 20,000 and 30,000 pages of communication between him and 37-year-old housewife Jill Kelley.

Jill Kelley entered the public eye when she was the target of threatening emails from Paula Broadwell, which the FBI used to uncover the affair between Broadwell and david Petraeus, leading to the former general’s resignation from the CIA.

John Allen, 58, who is married with two daughters, succeeded David Petraeus in Afghanistan and was due to take over as NATO’s top commander – his appointment has been suspended while his relationship with Jill Kelley is investigated.

John Allen, who graduated from the Naval Academy in 1976, was Deputy Commander of Central Command, based in Tampa, prior to taking over in Afghanistan. He also is a veteran of the Iraq war.

He lives in Washington D.C. with his wife, Kathy, with whom he has two daughters, Bobbie and Betty. Betty is a teacher, while Bobbie, a 27-year-old graduate of Virginia Tech, is a singer and released her debut album last year.

After growing up in Oakton, Virginia, John Allen graduated with military honors from the Naval Academy with the class of 1976. He is a 1998 distinguished graduate of the National War College.

John Allen holds a master of arts degree in national security studies from Georgetown University, a master of science degree in strategic intelligence from the Defense Intelligence College, and a master of science degree in national security strategy from the National War College.

General John R. Allen assumed his duties as the Commander, International Security Assistance Force – Afghanistan and United States Forces – Afghanistan on July 18, 2011.

John Allen played a key role in countering the Iraq insurgency between 2006 and 2008. He then oversaw a surge in US troops in Afghanistan in battling the Taliban.

In Afghanistan, General John R. Allen commanded coalition troops from 50 different countries.

He was nominated in October by President Barack Obama to be Supreme Allied Commander Europe and commander of the U.S. European Command – that is now on hold.

But if John Allen is found to have engaged in an extramarital affair – a crime in the military – he faces being court martialed, bringing a spectacular fall from grace and the end to a glittering army career that has spanned nearly 40 years.

President Barack Obama had nominated John Allen to take over as chief of the military’s European Command and NATO’s Supreme Allied Commander in Europe, but that nomination is now on hold as the Pentagon investigates Allen’s relationship with Kelley, Defense Secretary Leon Panetta told reporters.

John Allen had been expected to take that new post in early 2013 if confirmed by the Senate, as had been widely expected.

The FBI notified the Pentagon of its investigation into John Allen’s communications with Jill Kelley on Sunday evening, an unnamed senior defence official said.

Leon Panetta said he immediately notified the White House and top leaders in Congress of the investigation.

Leon Panetta said John Allen would remain as commander of U.S. and NATO forces in Afghanistan for now, “while the matter is under investigation and before the facts are determined”.

Pentagon officials have declined to comment on the nature of the relationship between Jill Kelley and John Allen except to say that it was “potentially inappropriate”.

Officials have not said whether any national security secrets were breached.