Funnyman Zach Galifianakis revealed a very creepy story about wearing Justin Bieber’s intimates instead of going commando.

The actor recalled the story to David Letterman during his appearance on “My Next Guest Needs No Introduction”, telling him the heist occurred back in 2014 after The Biebs appeared on his online interview show “Between Two Ferns”. Following the interview and after Bieber departed, Galifianakis took a shower in the “Sorry” singer’s dressing room after being “slimed” on camera.

“I had to change clothes,” he prefaces the story. “I got into his trailer to get this stuff off of me. I brought pants and a shirt and I can’t wear this underwear. So I see a pair of underwear in the corner. I needed a pair of underwear. But the fact that it was his was probably more interesting to me. I put ’em on and then I started thinking about it, on a lot of levels it’s wrong.”

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Letterman called it an “emergency” underwear situation as Galifianakis, 49, continues with his story, stifling laughs and reiterating his dire need cancelled out the “creepiness” factor.

“It has nothing to do with wanting to put Justin Bieber’s underwear on,” he says. “I’m questioning myself, I’m not 100 per cent sure why I did it. I took them off quickly.”

He may have taken them off quickly, but “The Hangover” star didn’t let go of the undies.

“I took the underwear,” he confesses. “Years pass, and I had taken the underwear with me… because I have nieces.”

“I’m sorry?” an incredulous Letterman asks before interrupting the story with laughter. “Oh no, ‘Girls, guess what, Justin Bieber’s underpants.'”

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Turns out, Galifianakis’ niece did not appreciate the 25-year-old singer’s underwear as a gift.

“I thought she’d be excited. I was like, ‘Hey, I’ve been saving these for you’ and the look on my niece’s face. She did not accept it. She was not into it at all. Which, I’m glad that she wasn’t,” he explains, adding, “My sister was excited like I was. She was into it.”

Watch the 2014 “Between Two Ferns” interview with Bieber below.