WASHINGTON, Nov 10: CIA Director David Petraeus was having an affair with his biographer Paula Broadwell, a reserve army officer, the US media reported on Saturday.

Quoting official sources, the media reported that the FBI discovered the relationship by monitoring Gen Petraeus’ emails, after it was alerted that Ms Broadwell could have had access to the CIA chief’s personal email.

Ms Broadwell’s book, “All In: The Education of General David Petraeus,” was co-authored with Vernon Loeb, a Washington Post journalist, and published in January. It is her first book.

Ms Broadwell, a 1995 graduate of the US Military Academy, West Point, New York, also has advanced degrees in public policy, international security and war studies.

The book grew out of her dissertation on transformational leadership and organisational innovation, using Gen Petraeus as a case study. Ms Broadwell’s photos with the general were part of the case study which took her to Afghanistan and Iraq.

The FBI investigation that led to the discovery of Gen Petraeus’ extramarital affair and his resignation on Friday began when someone reported suspicious emails allegedly from Ms Broadwell to the FBI. The agency then determined that she allegedly had emailed a number of government employees.

The FBI was at one point trying to determine whether any of the employees were being stalked.

Ms Broadwell told Fox News earlier this year that she met the four-star general when she was a postgraduate student at Harvard and he came to the university to speak.

They kept in touch via email and ran into each other again when she came to Washington.

“He gave me his card,” said Ms Broadwell. “We kept in touch.”

Ms Broadwell also called Mr Petraeus’ wife of 38 years, Holly Petraeus, “a wonderful military spouse”. The FBI investigation ended when the agency determined no criminal acts had been committed.

Mr Petraeus, who turned 60 on Wednesday, met his wife when he was a cadet at West Point. She was the daughter of the academy superintendent.

They have two children, and their son led an infantry platoon in Afghanistan.