“I screwed up royally.”

Probably not the best choice of words, but that’s how former CIA Director Gen. David Petraeus described the chain of events that led to his resignation following the revelation that he had an affair with his biographer Paula Broadwell.

Petraeus resigned earlier this month after the affair with Broadwell came to light. The revelation was uncovered following an FBI investigation spurred by Petraeus' friend Jill Kelley, who said she received “threatening” e-mails from Broadwell.

“I screwed up royally. I paid the price (appropriately) and I sought to do the right thing, at the end of the day,” Petraeus said of his resignation in a letter written to his friend, retired Brigadier Gen. James Shelton, the Daily Mail reported.

Shelton told the British tabloid’s website that he blamed Broadwell for the affair, which started when the 40-year-old married woman shadowed Petraeus for her book, “All In: The Education of General David Petraeus.”

“I never knew David as being a woman chaser -- he never gave a damn about anybody other than Holly,” Shelton said, referring to the erstwhile CIA director’s wife of more than 35 years. “It never entered my mind that he would get involved with anybody else. Paula was more savvy than Dave about the nature of the things that they got involved with.”

“I don’t believe he had any relationships with anybody else (apart from Broadwell),” Shelton continued. “He was the innocent one when it came to relationships. It wasn’t his bag. He was a soldier. He just wasn’t involved with it.”

In the letter, Petraeus said he believed he could overcome his stunning fall from grace and said he was grateful that Holly has not sought a divorce.

“Team Petraeus will survive though it has obviously created enormous difficulty for us. Holly is however once again demonstrating how incredibly fortunate I was to marry her,” he wrote.

While Petraeus stood by his decision to resign, his friend Shelton believed it was unnecessary for the former CIA director to step down.

He called the scrutiny of Petraeus following news of the affair an “overreaction” for “human things he got involved with.”