Diane, I've known David Petraeus for close to a decade and this news is truly stunning. There is no one in the military who is viewed as more disciplined and frankly more concerned with his own image and own career. But the seriousness of having a CIA director involved in an extra marital affair cannot be overplayed. 

As CIA director, Petraeus held all of the nation抯 secrets, but was keeping a big one of his own. Today in a statement to the CIA employees, the man considered a national hero by some acknowledged the affair and what he calls his extremely poor judgment. Such behavior is unacceptable, the statement said, both as a husband and as the leader of an organization such as ours. Petraeus went to the White House yesterday to turn in his resignation, the same place he has so frequently been called upon to serve. 

It抯 a great privilege to serve 

Today in a statement president Obama praised Petraeus?dedication and patriotism and said his thoughts and prayers are with Dave and Holly Petraeus. Holly and Dave Petraeus have been married 38 years, she was the daughter of the commando of West Point during Petraeus?years at the military academy. Petraeus went on to a distinguished military career in Iraq under George Bush抯 tenure

General David Petraeus was asked to do a very difficult job and he did it with distinction and honor. 

And then for President Obama into Afghanistan, and then the CIA. But that is why this is so troubling, certainly others have been involved in extra-marital affairs in congress and elsewhere, but having the director of Central Intelligence involved in an illicit affair with world leaders?friend and foe watching his every move and almost certainly looking for vulnerabilities and possibilities for blackmail. 

Petraeus did not reveal why he chose now to resign, but ABC News has learned that the FBI was investigating Petraeus?biographer, Paula Broadwell, for strange activity on the internet, when some emails were discovered that raised concerns. Broadwell抯 biography of Petraeus is called ALL IN, the education of general David Patraeus, a book she spoke about on John Stewart earlier this year. 

I have been working on this project as my dissertation and when he went to Afghanistan in the summer of 2010, I decided to turn it into a book and I shot him an email and said I抦 gonna go for it and I抦 not sure he took me seriously, but I showed up in Afghanistan, and sent him an email said I抦 doing this, and he said I was showing hardship with the troops, and said go for it. So, but as you know, my background is the mili-band. 

He trusted you (I think so)a little bit more.

I spoke to a friend of Petraeus?this evening who had been in touch with the director today, he said Petraeus does not blame anyone but himself. Diane.

Marsa Raddatz reporting and now we go to ABC抯 White House correspondent Jake Tapper,  here to tell us whether the White House is saying tonight, Jake. 

Well, Diane, senior White House officials tell me that the overwhelming emotion here is surprise and of course sorrow for a colleague and his family. The White House officials were told about this on Wednesday, the day after President Obama was re-elected, they were told by the director of national intelligence James Clamper on Thursday. President Obama was informed about the situation, the entire situation, the FBI investigation as well as the affair, general Petraeus called the national security advisor Tom Dalen said he wanted to talk with the president. At that meeting yesterday he offered to resign, President Obama thought about it, conferred with ayes. And today called Petraeus and accepted that resignation, the new acting director of the CIA will be the No. 2, the deputy director Mike Mural with whom president Obama has worked closely during the Osama Bin Laden raid planning for instance, and he has the inside track. But this does come in at an awkward time for the CIA, they are going to be called to congress next week to talk about what went wrong at Benghazi, and of course, the CIA is under constant pressure because of the threat of terrorist attack, Diane.