Feinstein tells "Fox News Sunday" that she first learned about the matter from the media late last week. Feinstein says she called Petraeus twice on Friday and was dumbstruck when he acknowledged the affair.
The California Democrat says the news was "like a lightning bolt."
Feinstein says she's now been briefed by the FBI but wants to know why the bureau didn't notify her sooner because of the national security implications.
Feinstein says she initially didn't want President Barack Obama to accept Petraeus' resignation, but realizes now he had no choice.
(Copyright 2012 by The Associated Press. All Rights Reserved.)