Watch Howard Stern try to kiss David Letterman

Howard Stern paid a visit to CBS' "Late Show" Monday night -- and he seemed to catch host David Letterman off-guard when went in for a kiss on the lips.

The old friends chatted about everything from retirement to a canceled dinner and the best guests on their respective shows.

At one point Stern beckons Letterman to "come over here." Letterman -- clearly skeptical ("What are you doing" he asks) -- comes out from behind his desk before Stern says "Is this goodbye? Is this our final time together?"

Stern then proceeds to kiss Letterman on the lips.

"What are you going to do?" Letterman asks again.

Watch it unfold below:

Stern is among the final guests on the "Late Show with David Letterman," which airs its final episode on May 20. Stephen Colbert will be taking over hosting duties.