Welcome back, Uma!

Uma Thurman was back in her gala finery in NYC on Wednesday evening, attending her very first red carpet event since welcoming her third child, a baby girl, in mid-July.

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The Smash actress and former model, 43, looked serene and impressively slim at the Annual Brazil Foundation Gala Party at the American Museum of Natural History. Thurman wore a deep purple, floor-length silk gown with a plunging neckline.

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At the svelte-again star's side was on-again financier love Arpad Busson, the father of Thurman's baby girl, whose name has yet to be revealed to the public. The twosome began dating in 2007, called off an engagement in 2009, and finally reunited in 2011.

Their daughter joins siblings Maya, 13, and Levon, 10, Thurman's kids with ex-husband Ethan Hawke.

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"Uma was definitely not planning on having another kid," a source said when Us broke the news of her pregnancy in February. "It was a surprise, but she's over the moon about it. Very excited."

This article originally appeared on Usmagazine.com: Uma Thurman Debuts Slim Post-Baby Body on Red Carpet