This photo, supplied by CBS, shows actor Vince Vaughn visiting with CBS' David Letterman during an interview that involved a discussion about his relationship with Jennifer Aniston during the taping earlier this week of 'The Late Show with David Letterman' that will be aired Friday, May 5, 2006, (AP Photo/ John Paul Filo,CBS)

Though Vince Vaughn and Jennifer Aniston have been mum about their romantic relationship, they aren't fooling David Letterman.

With Vaughn as a guest on "The Late Show," Letterman took the approach of presuming the relationship, which has been frequently photographed, but not "officially" confirmed.

"Hey, nice going on that Jennifer Aniston thing," the late-night host says to Vaughn on a taped interview to air Friday on CBS (11:30 p.m. EDT).

Letterman also tells Vaughn, who stars with Aniston in the upcoming film, "The Break-Up," that he thinks they make a nice couple.

An embarrassed and amused Vaughn responds: "It's very nice of you to say that, Dave, thank you. Yeah, it's been kind of interesting for me, and I just choose not to talk about my private life that much publicly."

As the conversation continues, the 36-year-old actor eventually addresses the audience, "Do you like the way he just kind of takes the approach that it's fact?"

Letterman then asks if they aren't a couple.

"I'm not saying we are or aren't a couple," says Vaughn. "I think she's great, but I just don't discuss whether we are."

Reports of a relationship between Vaughn and Aniston, 37, began to surface last fall when the two were shooting "The Break-Up." Neither star has confirmed it.

Aniston was divorced from Brad Pitt last October.