But first, some jokes!
"You know, over the years, I have talked one or two times about Fox News host and bold, fresh piece of humanity Bill O'Reilly," Colbert, the actual, said in his Late Show monologue.
Colbert continued: "He's been a guest on this show, and I take no pleasure in his downfall. OK? I'm not going to sit here and publicly gloat."
The audience giggled.
"Jimmy, can you take the camera off me for just a second?" Colbert said.
The camera panned to Colbert's desk.
Colbert made a gloating sound.
The audience roared.
"This is huge," he said. "It's like looking at your front yard and the big oak tree is just gone. And sure, the oak tree said some disturbing things about young black men, what with their rap music and their neck tattoos.
"But dammit, the tree had been there forever. And your grandpa liked to just sit there and stare at it. And then the tree would sell your grandpa gold coins and self-lubricating catheters."
Colbert then acknowledged the obvious.
"Here's the thing: I owe a lot to Bill O'Reilly," he said. "I spent over nine years playing a character based largely on him — and then 12 months in therapy to de-bloviate myself.
"So tonight, we at The Late Show are proud to issue a statement from Bill O'Reilly's biggest fan: Conservative pundit Stephen Colbert."
On The Late Show's YouTube channel, the caption for said statement reads: "A brash, loud-mouthed, far-right know-it-all has some parting words for a brash, loud-mouthed, far-right know-it-all."
Yep.
"Hello nation — and shame on you," said Colbert, the character with the arched eyebrow.
"You failed him; you failed Bill O'Reilly. You didn't deserve this great man. All he ever did was have your back — and if you're a woman, have a go at the front, too. And what, suddenly sexual harassment's a crime? But that's the country we live in now: Obama Trump's America."
He invited O'Reilly to join him and Jon Stewart at their mountain cabin.
And then he choked up, adding: "Stay strong, Papa Bear."
O'Reilly appeared numerous times on The Late Show, on which Colbert called him "a cable-news superhero."
"You've been on my show four times now," Colbert said to O'Reilly in October. "And I always start with the same question: Bill, what the hell is going on?"
But their most memorable meetings took place a decade ago, during crossover appearances on Comedy Central and Fox News on January 18, 2007.
As the Associated Press noted at the time: "Parody met its inspiration ... when Stephen Colbert and Bill O'Reilly traded guest appearances on each other's shows in an exchange that Colbert called 'a meeting of the guts.'"
"This was a huge mistake, me coming on here," O'Reilly said that night in Colbert's studio, which, the AP reported, was "decorated for the occasion with a large 'Mission Accomplished' banner and a portrait of O'Reilly placed fireside."