WASHINGTON -- My wife says I’m the most clueless person in America.

I never anticipated the extramarital affair between David Petraeus and Paula Broadwell, the woman I’d worked with for 16 months on a book about Petraeus’ year commanding the war in Afghanistan. On rare occasions, her good looks and close access would prompt a colleague to raise an eyebrow about their relationship, but I never took it seriously.

I certainly wasn’t alone. The unusually close relationship between subject and biographer was no secret by the time President Obama nominated Petraeus as CIA director in the summer of 2011 following his command year in Kabul. America’s most famous and heralded general had granted Broadwell extraordinary access for her book, All In: The Education of General David Petraeus. Nor has Broadwell done anything to hide this access or her great admiration of Petraeus since the book was published in January, describing him in terms that are, well, effusive.

So when the news broke that Petraeus was resigning in disgrace because of an adulterous affair, I was dumbfounded. “Could it be Paula?” my friends and colleagues asked immediately. Even then, I said I would give her the benefit of the doubt — until the doubt evaporated a few hours later.

I came by my ringside seat on this epic Washington scandal innocently enough: In July 2010, I got a call from my agent, Scott Moyers in New York, who wanted to know whether I was interested in ghostwriting a war book about Petraeus, who had just been named commander in Afghanistan. I’d just finished ghostwriting a CIA memoir that Scott had represented.

He described his other client, with whom I’d be working, as a woman who had unique access to Petraeus. She was, in Moyers’ telling, a dynamo — a West Point graduate who’d worked in counterterrorism after Sept. 11 and was pursuing a Ph.D. at King’s College in London. It sounded like an incredible opportunity.

As Pentagon correspondent for The Washington Post, I had briefly embedded with the 101st Airborne Division under Petraeus’ command in northern Iraq in the fall of 2003, and found the general — and what he’d accomplished — impressive and inspiring. Mosul, and much of his sector in the north, were largely pacified, and Petraeus granted me unfettered access to his command headquarters and his battalion commanders. We even went running together around one of Saddam’s demi-palaces in Mosul, where his command was bivouacked.

The fact that I was a runner seemed to Moyers to make me the perfect fit for the job. He joked, when he was introducing me to Broadwell, that I was the only ghostwriter who could run with Petraeus — and with Broadwell. Both were ultra-competitive distance runners who prided themselves on speed, and both could do hundreds of push-ups.

I flew to Charlotte and spent an afternoon sifting through an impressive pile of e-mails and documents on Broadwell’s dining room table that she had already compiled as part of a Ph.D. thesis she was writing on Petraeus and his approach to leadership, which he had agreed to help her with after they met at Harvard a few years earlier.

What was she like? Professional, relaxed and clearly excited about the material she had for me in her big, comfortable house in a stately North Carolina neighborhood. She spoke with great affection about her husband, a surgical radiologist whom she’d met in the military, and her two young sons, whom she clearly adores.