Fox News has confirmed the identity of the FBI agent who started the investigation that led to Friday's resignation of Gen. David Petraeus as CIA Director.

Fred Humphries, 47, was contacted by Jill Kelley - described by the media as a Tampa, Fla., socialite - who reported receiving harassing emails that later turned out to be coming from Petraeus' mistress, Paula Broadwell.

Humphries was also alleged to have sent shirtless photos of himself to Kelley at one point. But his lawyer said those photos were "benign," and sent years prior. He also said Humphries and his wife are friends with Kelley and her husband.

Learn more about Humphries in Jennifer Griffin's report, including which famous terror plot he was involved in breaking up.