David Petraeus, the former CIA director who recently resigned from his post after an affair with his biographer Paula Broadwell was revealed, told a colleague and former mentor in a letter that he “screwed up royally”.

Petraeus has largely kept out of the spotlight since the affair was revealed and hasn’t commented on the ordeal, so the letter comes as a revelation to those who know some of the details of the story. In it, he says that he understands the trouble he has put his family through and that he sees, once again, how lucky he is to have his wife Holly.

“I paid the price, appropriately,” he wrote in the letter to retired Brigadier General James Shelton, in response to a note of support from his old friend.

Shelton says he was shocked when the news was made public and, though he never met Paula Broadwell face-to-face, claims he found her to be very engaging and bright during their phone conversations (he was a source for her while she was writing her book about Petraeus).

“I don’t think he was expecting to happen, what happened…I don’t think she wove a web around Dave and dragged him in. I don’t think that at all. I think it was mutual…he wasn’t looking for it. It happened.”