The 82-year-old actress recalled on the CBS late-night program how Stewart, her idol, surprised her by showing up to the finale of "The Carol Burnett Show" in 1978. Decades later, Colbert had a similar surprise up his sleeve.
"Well, there's actually somebody here tonight, and you are his idol," Colbert told Burnett, "and it's the actor Kevin Spacey, and he would like to come out and say hi."
Spacey came out and almost immediately started impersonating Stewart, who passed away in 1997 at the age of 89. The 56-year-old even read a poem as the actor once used to do on Johnny Carson's "Tonight Show."
The sweet, silly poem brought tears to Burnett's eyes. "The drinks are on me all night at the bar," Spacey, as Stewart, recited as Burnett became emotional, "because Carol Burnett is still comedy's greatest star."
Spacey had another great moment during his appearance on "The Late Show." He revealed to Colbert just who he imagines he's talking to when his "House of Cards" character, Frank Underwood, turns to the camera.
"Who is that person? Is it like a close confidant," Colbert asked. "Because, the person you're actually talking to, of course, are the people on a 10-hour Netflix binge sucking on box wine."
"I'm talking to one person and one person only," Spacey revealed. "And that is Donald Trump."
"I think he's getting the messages," Colbert responded.