Jon Stewart asked Stephen Colbert how he found his ‘Late Show’ voice. The answer? Joe Biden.

Stewart’s intermittent appearances on “The Late Show” are undoubtedly delightful for fans of “The Daily Show” and “The Colbert Report,” the spinoff Colbert hosted for nine years. But Tuesday’s segment was extra special, because it marked only the second time Stewart had ever interviewed Colbert.

The two men reminisced about the first instance — a 2001 “Daily Show” interview in which Colbert answered questions as the Rev. Al Sharpton, who had canceled his appearance on the show. (Colbert has previously mentioned the segment as one of his favorites.)

“And it was so brilliant that Al Sharpton’s Action Network actually asked Stephen to take over,” Stewart joked.

Stewart talked about how Colbert had built a unique career in comedy by taking on personas like the conservative he played on “The Colbert Report.”

“What was it like to then pull off all of the character, all of the facades?” Stewart asked. “All of the characters you played were incredibly opinionated. When you first came out here, the vulnerability you felt expressing opinions that people knew that they could peg to you, how hard was that?”

“That was one of the challenges. One of the challenges is that, oh, if I say it, it’s really me saying it, not a character. You don’t have the protection of the mask,” Colbert said. “Which I worked so hard to never let go at the old show.”

Colbert added that before he would walk out on stage at the Comedy Central show, he would slap himself in the face — “hard, twice, and the rule was I had to slap myself hard enough to regret having done it,” he said — to remind himself never to break character.

Colbert explained that for the first few months of “The Late Show,” his wife, Evie, would sit in the audience as a reminder that he was Stephen Colbert — not his character from “The Colbert Report,” whose wife was called Lorraine.

“But I was completely uncomfortable just standing out there and telling jokes,” he confessed. “We didn’t really do a proper monologue for six months.”

“Do you remember what moment allowed you to confidently step into who you really are hosting this show and when it happened?” Stewart asked.

“For the interviews, I got there a little bit quicker, though not consistently,” Colbert said, mentioning former vice president Joe Biden’s 2015 appearance, just months after the death of Biden’s son, Beau.

“Only I, my real self, could have received what Mr. Biden was willing to share with me and with the audience,” Colbert said.

“Exactly,” Colbert said. “And when he left I turned to [executive producer Tom Purcell] over there, and I said that nice old man just gave me my show because I know there are times that I absolutely have to be myself.”

Colbert also talked about the moment he decided to do a monologue, which Stewart helped him realize didn’t have to completely buck the traditional late-night mold.

“In the six weeks you’ve been thinking about doing this show, you haven’t replaced the most recognized form of something that has existed for 60 years?” Colbert recalled his colleague jokingly asking.

“We were trying to do something that hadn’t been done before,” Colbert explained. “And here, what I’ve discovered is that I can have so much fun doing an old form but with our flavor.”

Ultimately, Colbert said it was the live shows that helped him get comfortable telling jokes in his own voice.

“Live shows gave everything immediacy. And then I knew, ‘Oh, I know how to do this show now, ‘” Colbert said. “You have to do it with immediacy and with urgency and all those things we took to the old work through the character. But now I just have to say it as myself.”

And even though Stewart was in the interviewer chair, Colbert couldn’t help but ask his friend a question. Does he miss hosting “The Daily Show” now that Trump is in the White House?

“Working at ‘The Daily Show’ I felt as though I was toiling in the turd mines, and then I finally quit and a giant turd asteroid heads toward the planet,” Stewart explained. “In that instance, if someone said, ‘Hey, you were a turd miner — this is the largest turd deposit ever seen. Don’t you wish you were in there?’ ”

Stewart threw his hands up. “I’m out of the turd business. I’m out.”

“Come on in, Jon,” a smiling Colbert replied. “The turd’s fine.”