By Chris Nashawaty
Updated September 29, 2010 at 01:21 PM EDT

For anyone who’s been following the ongoingly frosty and seemingly endless feud between David Letterman and Oprah Winfrey, last night’s Late Show provided new insight into their long-standing Cold War. Chatting with guest Jon Stewart, Letterman revealed that the iciness dates back much further than Letterman’s notorious (and notoriously awkward) joke while hosting the 1995 Academy Award telecast: “Oprah, Uma…Uma, Oprah”. In fact, Letterman told Stewart — and the insomniacs watching at home — that the real cause of the rift was a practical joke Letterman played on Winfrey long before he laid his Oscars egg.

Turns out that Letterman and his then-girlfriend, Regina Lasko, found themselves having lunch in the same restaurant as Oprah and Steadman while on vacation. As a gag, Letterman told the waiter that Winfrey’s table was picking up their check. Apparently, Winfrey didn’t find this as hilarious as Letterman did.

Stewart, who was Letterman’s guest, actually turned the tables on the Late Show host, getting the ever-secretive Letterman to reveal more about himself than the person sitting in his hot seat — the sign of a great late-night talk show couch sitter.

“In the beginning Oprah frightened me,” said Letterman. When asked why, he replied, “because she could squash me like a bug. She could put me out of the business. And she hated me, that’s what it was.”

Check out the clip from last night’s show to see more about “The Incident” and why Letterman, in all of his wonderfully creepy insecurities, remains must-watch TV.