Britney is looking fantastic, and her workouts have paid off.

Britney Spears played it for laughs on Monday night's Late Show with David Letterman. Sporting a blonde bob and a short black dress that showed off her newly svelte shape, the new mom – whose second son, Jayden James Federline, was born Sept. 12 – surprised the host by walking onstage behind him as he was sitting at his desk. "Oh, my god," he exclaimed, standing up to shake her hand and plant a kiss behind her ear. "Hi, how are you? Nice to see you. Oh, you look wonderful." "Thank you so much," she said. "I'm in town, and I'm just such a huge fan. I had to stop by." "That's very nice of you to say," said Letterman. "That means so much to me." Said Spears: "Uh, no, I wasn't talking about you. I was talking about Will Ferrell." A flustered Letterman then quickly directed her to the whereabouts of his guest for the evening: "In the green room."

(TMZ & People)
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