30 Rock on, girl! Tina Fey looked positively gorgeous during her appearance on the Late Show With David Letterman on Thursday, May 7 — so gorgeous, in fact, that Letterman himself couldn't help commenting, even at the risk of sounding "indelicate." Her secret? Spanx, which she revealed by stripping down on camera.

"I realized that when you retire, this is it. Like, I'm never gonna wear a fancy dress on a talk show again," she told the departing CBS host. "First of all, it's very hard work. I don't know if you're aware of the contraptions under here. It's almost medical."

She went on to say that Letterman — who will hand over the Late Show to Stephen Colbert this fall — is the only late-night host for whom she'd wear a fancy frock.

"I dress up like this out of respect for you. I really do," the 30 Rock alum, 44, shared. "But this is it...Am I gonna put a dress on for Jimmy [Fallon]? That's creepy. He's like my brother. I'm gonna wear special underwear for James Corden? That's not gonna happen. So the next time you see me, I will be playing charades in a slanket."

Standing up to fully show off her figure-flattering blue dress, she added, "Because this is my last time wearing a fancy dress on a talk show and conforming to gender norms out of respect for you, my gift to you is, I want to give you the dress."

She then asked Letterman to help her unzip before undressing onstage to reveal her nude bra, thigh-shaper, and black slimming bodysuit, which read, "Bye Dave!" and "#LastDressEver" on the front and back, respectively.

Letterman — and his studio audience — went wild. "Oh my god! I don't know what to say," he quipped, laughing. "Oh, for heaven's sake!"

Watch the clip above!