Philbin, a legendary television personality, died at the age of 88 in July. Letterman was friends with Philbin who appeared on his late night talk show multiple times, previously calling him the best guest he ever had.
"I kind of believe he is, was, the last connection to a show business that I grew up watching back in Indiana," Letterman said on Wednesday.
"When Regis left us, to me it seemed like okay that chapter is closed. And that made me very sad. But I'm telling you, this guy, if somebody said let's pick somebody to drive cross country with, if it couldn't be Regis then I would hitchhike because he was always Regis," he continued before Kimmel agreed with him.
"Regis was just exactly like he was on television at all times, which is really remarkable. It's very unusual," Kimmel said.
Letterman praised Philbin for never saying no to anything he wanted to do on his show.
"He never said no and he often would do things that we didn't want him to do. He showed up once dressed as Shrek and I don't know why. I'm not sure he knew why, but there he was in his Shrek outfit, but I was unimpressed. I mean there are guys in show business who need the costume to stay in business. Regis was not one of them," Letterman said as Kimmel laughed.
Season 3 of Letterman's new talk show My Next Guest Needs No Introduction recently arrived on Netflix. Letterman interviews Dave Chappelle, Kim Kardashian, Lizzo and Robert Downey Jr. in the new batch of episodes.