The shock jock has been appearing on Letterman's talks shows since 1984. Those appearances turned into an off-air friendship in the 1990s -- that is, until Stern would reveal their private conversations on air. Even though Stern kept appearing visiting Letterman's show, he didn't formally apologize until 2011 during a Late Show visit. "I've apologized to a lot of people. And I'll tell you why. I think I did a lot of growing up," Stern told Letterman. "And I do attribute this to psychotherapy. I was just a young man full of rage. Through psychotherapy I started to fall in love with life a little bit. I started to appreciate what was good. … one of those things was my relationship with you. I could appreciate what you had done for me. I had betrayed your trust, and I was ashamed. The reality was I loved you, and I really felt strongly about you." ALSO: Stern reveals Donald Trump asked him to speak at the Republican National Convention.