(CNN) -- The affair that brought an end to David Petraeus' tenure as CIA director came to light during an FBI investigation into a complaint that his biographer Paula Broadwell was sending harassing e-mails to another woman close to him, a U.S. official said Saturday.
During the investigation, other communications surfaced between Petraeus and Broadwell, a married mother of two, according to the official.
The official did not identify the woman who made the initial complaint and did not know the nature of her relationship with Petraeus.
The FBI interviewed Petraeus in the course of its inquiry, said the official, who stressed that the CIA director was never the target of the investigation and his communications were never compromised. The official did not know whether Broadwell was interviewed.
The official did not have an exact timeframe for the investigation and could not say if it is still ongoing.
CNN has not been able to reach Broadwell for comment.
The Obama administration first learned of the affair in a phone call from the FBI to Director of National Security James Clapper at 5 p.m. on election night, according to a senior U.S. intelligence official.
On Saturday, questions arose about why congressional leaders were not informed of the investigation immediately.
According to a congressional aide familiar with the matter, the House and Senate intelligence committees weren't informed that there was an FBI investigation into Petraeus until Friday.
"The committees are required to be kept informed of significant intelligence activities," the aide said Saturday. "If there was an official investigation that was looking, at least in part, at information that was compromising the CIA director, then I think there's a solid argument to say that the committee leadership should have been notified to at least some level of detail."
The resignation also comes days before Petraeus was slated to testify before the Senate Intelligence Committee about the September 11 attack on the U.S. Consulate in Benghazi, Libya. The attack, in which four Americans were killed, became a point of contention during the presidential campaign.
Some have even suggested that the timing of Petraeus' stepping down is suspect, given the expected grilling in Congress. Acting CIA Director Michael Morell will testify instead. Source CNN NEWS
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