Vernon Loeb, the ghostwriter behind Paula Broadwell's glowing biography of former Gen. David Petraeus, said in an op-ed that he was "clueless" about the affair between them and always wondered why she received such close access to the now-disgraced CIA director.

After days of silence -- during which he turned down multiple interview requests -- Loeb, a senior editor at the Washington Post, penned a first-person account [5] of his time working with Broadwell on the Petraeus book.

"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," he wrote in the op-ed, published Tuesday. "So when the news broke Friday that Petraeus was resigning in disgrace because of an adulterous affair, I was dumbfounded."

Since Petraeus resigned, details have trickled out about his extramarital affair with Broadwell, which came to light after the biographer allegedly sent a series of harassing emails to another woman, Jill Kelley, an Air Force liaison in Florida.

Kelley's complaints launched an FBI investigation, which, as of Monday night, expanded to include Gen. John Allen, the commander of U.S. forces in Afghanistan and a nominee for the top rank in NATO's coalition in the country.

Also read: David Petraeus Bio Co-Author to Speak Out on Broadwell Sex Scandal [6]

Loeb said that while he authored "All In: The Education of Gen. David Petraeus" from his basement office in Maryland, he was fed a "torrent" of emails and other material Broadwell  gathered while spending time with the general in Kabul.

"I had no say over the book’s ultimate take on Petraeus, which some have found excessively laudatory," Loeb wrote. "Broadwell was free to make whatever revision or modifications she desired to the text, and did so liberally."

Still, when Loeb's colleagues "raised eyebrows" at the flashy cocktail dresses she wore at staid diplomatic gatherings, he brushed it off. Petraeus had long preached to his protégés that someone is always watching, and Loeb said the two were not overtly affectionate in public.

Loeb's access to Petraeus was limited. He said they once went jogging in Washington, access he scarcely believed he would ever have and that he now believes is rarely offered for purely ethical reasons.

"I never thought they were having an affair -- and I still have no idea when the affair actually began," Loeb wrote. "I sent Broadwell an e-mail Monday, letting her know that I was writing this piece and welcoming any comment she chose to make. I have yet to hear back from her."