Not long after David Letterman made a public apology during Monday's episode, more scandalous details about his affair with 'Late Show' staffer Stephanie Birkitt started to surface -- including diary excerpts about their sexual relations.

Birkitt's diary revealed that she and Letterman enjoyed romantic hikes last fall at his sprawling ranch in eastern Montana -- where he was married in March -- while her boyfriend Robert "Joe" Halderman stayed home in Connecticut, sources told The NY Post. While she tried to keep it a secret, Halderman eventually found Birkitt's diary in December and learned she was still carrying on a steamy affair with Letterman.