"That whole thing was my fault. You know, I'm sorry," Letterman said to Oprah on Thursday. CBS David Letterman apologized again to former frienemy Oprah Winfrey on Thursday.

It was Oprah's first appearance on "Late Show" since December 2005. She returned to promote her upcoming film, "Lee Daniel's The Butler."

The two were reportedly feuding for more than 20 years. It started in the late 80s when Oprah had an uncomfortable first-time experience on "Late Show." She refused to be a guest again, causing Letterman to crack jokes at her expense and perpetuate exaggerated rumors of Oprah's hate for him.

Letterman also admitted to once sticking her with a restaurant bill, even though the pair weren't dining together.

"She was with Steadman, I was with my then-girlfriend Regina. We were both at a restaurant having lunch on vacation. I said to Regina, 'Oh, this is hilarious, I'm gonna make Oprah buy us lunch,'" Letterman told Jon Stewart in 2010. "We got a free lunch and that's where it started."

They've since buried the hatchet — many times over. Oprah and Letterman made amends during her 2005 "Late Show" appearance, during an interview at Ball State University last fall, and again on an episode of "Oprah's Next Chapter" in January.

Thursday on "Late Show," they discussed the movie, her recent trip to Tanzania and meditation.

Late in the interview, Oprah detoured to reflect on how far they've come in their relationship.

Oprah: Aren't you pleased at how we've grown?

Letterman: Uh-huh?

Oprah: It's been like eight years! I mean, the last time I was here I was so nervous, and then you were so nice to me.

Letterman: Well that whole thing was my fault. You know, I'm sorry.

Oprah: I know, you already said you're sorry. You said you're sorry when I had you on my show.

Letterman: But I still feel lousy.

Oprah: No, no, don't even worry.

Watch the clip:

And here's the full interview: