WASHINGTON – David Petraeus, the retired four-star general renowned for taking charge of the military campaigns in Iraq and then Afghanistan, abruptly resigned Friday as director of the CIA, admitting to an extramarital affair.

The affair was discovered during an FBI investigation, according to officials briefed on the developments. They spoke on condition of anonymity because they were not authorized to publicly discuss the matter.

Petraeus carried on the affair with his biographer and reserve Army officer Paula Broadwell, according to several U.S. officials with knowledge of the situation. They spoke anonymously because they were not authorized to discuss the investigation that led to the resignation publicly.