'I screwed up royally,' Petraeus writes to old Army chum

/ Former CIA Director David Petraeus. By Mike Brunker, NBC News "I screwed up royally … (but) Team Petraeus will survive," former CIA Director David Petraeus wrote in a letter to an old Army chum after resigning his post and admitting to an extramarital affair, NBC News has confirmed. The letter to retired Brig. Gen. James Shelton, dated Nov. 20, was first reported Wednesday by Britain's Daily Mail newspaper.  In the letter, Petraeus thanked Shelton  for sending him some pictures and a note saying he still had faith in him despite the scandal that lead to his resignation.  "I screwed up royally. I paid the price (appropriately) and I sought to do the right thing, at the end of the day," it read in part. "Team Petraeus will survive though have obviously created enormous difficulty for us. Holly is however once again demonstrating how incredibly fortunate I was to marry her." Davis Turner / Reuters Paula Broadwell,leaves her home in Charlotte, N.C., on Nov. 19. Petraeus resigned his post on Nov. 9, citing an extramarital affair. Government and law enforcement officials have told NBC News that the 60-year-old former commander of U.S. and NATO forces in Afghanistan and coalition forces in Iraq was involved with his 37-year-old biographer, Paula Broadwell, who also is married. Shelton, 76, a longtime friend of Petraeus who described himself to the Daily Mail as a father figure to the former CIA director, told the newspaper that he never considered Petraeus "a woman chaser" and that Broadwell, who interviewed him for her book "All In," was "more savvy than Dave about the nature of the things that they got involved with." "She's not a kid. In a lot of ways I think she knows more about the world than Dave – I'm talking about sex," he said. "I don't think Dave ever thought about that too much, he only thought about the Army and gave it everything he had." NBC News' Amanda Sidman contributed to this report. More content from NBCNews.com: Did you wake up rich? Two winning Powerball tickets sold 11 things more likely to happen than winning the Powerball jackpot Neighbor charged with murder, rape of Jersey Bridgeman, 6 Florida man pleads not guilty to shooting teen to death over loud music 'Truce is over': Fired-up congressional panel vows strict VA oversight Video: Jill Kelley hires high-powered legal help Follow US news from NBCNews.com on Twitter and Facebook