Jimmy Kimmel, right, broadcasting his ABC show from Brooklyn this...

Jimmy Kimmel, right, broadcasting his ABC show from Brooklyn this week, interviewed retired late-night legend David Letterman on Tuesday, Oct. 17, 2017. Credit: ABC / Randy Holmes

The beard is still long, nearly flowing, and white. Blazing white. You almost need sunglasses to admire its bounty. Also, the guy behind it is still funny, sharp, odd, querulous, interesting, and engaging. Dave, oh Dave, where have you gone (and what exactly are you doing there, anyway)?

Returning to late night for the first time since retiring in 2015, David Letterman offered something of an answer on Tuesday’s “Jimmy Kimmel Live: Back to Brooklyn,” from the Howard Gilman Opera House at the Brooklyn Academy of Music.

For example, he’s got sartorial challenges, but let him explain. Acknowledging the applause (“thank you, thank you everybody”) he then promptly went downbeat: “You’re looking at a man who’s laughing on the outside but crying on the inside. For a year I’ve been looking high and low and can’t find a shirt that looks good untucked.”

Letterman, 70, doesn’t do late-night or any TV for that matter — not quite a hermit, but not fully engaged with the human race, either. “Tonight on Jimmy’s show,” he deadpanned, “he’s talking to an aging vagrant.” Therefore the questions almost asked themselves. Kimmel, 49, tried, in a valiant effort akin to nailing Jell-O to the wall.

Does Dave miss late night? Dave paused, then considered his response. He appeared ready to nod “yes,” then decided otherwise, then thought again before the light suddenly went off: “I miss wearing makeup.”

Letterman began this return engagement with a stemwinder anecdote about the horse he gave fellow late-night talk show host Conan O’Brien after Letterman retired. The horse, he explained, was meant to become a quick joke: O’Brien would bring the horse on stage at his show, where it would proceed to relieve itself, and then O’Brien would return the “gift.”

“Days later, I realized something had gone terribly wrong. I got this lovely letter from him saying his wife has decided to keep it because she’s an equestrian. . . . ”

Letterman said her decision put him in a tough spot: “I was counting on him to return the horse.”

At one point, Kimmel appeared to locate that elusive Letterman heart, saying, “I heard you say, ‘I’m a bit of a different person since retiring.’ ”

Letterman said, “Each and every day, if you take a look at the horizon of humanity [and say], ‘My God, is there anything we can do big or small to make the life of one person a little bit better?’, [then] that’s no small accomplishment.”

That, for some reason, reminded him of another story. He was recently traveling in southern Indiana, possibly as part of research for his new Netflix show (bowing next year), although he didn’t say. He went to a local bar to ask the patrons about a complicated bit of local lore and, upon opening the door, a “huge man” stood in his way.

The guy sized up Letterman, then said: “Oh my God, for the last 20 years I’ve seen you and changed the channel. And now here you are!”

Letterman said he told him, “Changing the channel doesn’t kill a person.”

Kimmel wondered how this was “helping make people’s lives better?”

“Baby steps,” he replied.

Kimmel pressed him on that new Netflix interview series, and whether he’s lined up guests. Letterman, who does not take to pressing readily, said: “You know that guy who saws a rowboat in half and seals it back up? We’re all set to go.”

Letterman will be awarded the Mark Twain Prize for American Humor on Sunday night at the Kennedy Center in Washington.

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