@kourtneykardash / Instagram 1 / 10
@kourtneykardash / Instagram 1 / 10

Whoa! Take a good look at Kourtney Kardashian. Really, look at her. The eldest Kardashian showed off her tight tummy and fit physique on Instagram on June 18.

Did we mention that Kourtney gave birth to her third child six months ago?

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The 36-year-old wore a black athletic bra and striped pajama bottoms in her latest selfie, bearing her abs and toned body.

"Hopped up out the bed, turn my swag on Took a look in the mirror said what's up?" she captioned the photo, quotes lyrics from Soula Boy's "Turn My Swag On."

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Since welcoming baby Reign, Kourtney has often posted photos to her Instagram account indicating that she's working on her fitness. Well, it's clearly working.

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In late April, Kourtney posted an image of a scale showing her weight at 116 pounds.

Hey Kim Kardashian, if you're wondering how to stay "on fleek" in the future, just ask your older sister.