Kylie Jenner has often claimed she doesn't work out, despite having a killer figure.

The Keeping Up With The Kardashians, who flashes the flesh more than her sister Kim these days

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flaunted her curves in a stunning bikini selfie on Instagram for fans.

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Posing in front of her bathroom mirror and holding her mobile phone up to take a snap

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she can be seen looking serious and pouting in the tiny black two-piece.

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She's clearly helping to cheer up her big sister Kourtney, following her split from

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long-term partner Scott Disick as the pair planned a 'swim session'.

Kylie, who turns 18 on August 10, looked older than her years and

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simply captioned the photo: "Kourt and Ky swim session.

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