Elizabeth Banks looked gorgeous as she arrived to the Ed Sullivan Theater in NYC to tape her appearance on Late Show With David Letterman yesterday. 

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The What to Expect When You're Expecting star shared a photo of her very pregnant sister with David Letterman and the audience — but this wasn't just any old photo. Elizabeth and her sister Sarah were in matching wetsuits, swimming with whale sharks, aka "the largest fish in the ocean," at a Georgia aquarium. 

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Of course funnyman David couldn't help put poke fun at heavily pregnant Sarah, saying, "Are they [whale sharks] bigger than your sister?" OUCH! 

We're sure Elizabeth is going to hear the wrath of her sister once she sees what went down on Late Show

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