Here's Gwyneth Paltrow and Chris Martin's daughter Apple Martin at the beach in a bikini ... and she can sure wear the hell out of some skimpy swimwear.

The 21-year-old celebuspawn hit the sand in the Hamptons this week with nothing but a gingham-print string bikini ... and the triangle top and matching bottoms looked darn good on her.

Apple got soaked playing in the waves ... and it looked like she had a blast on a beautiful day at the coast.

Frontside, backside ... Apple's got it down ... and we're not talking about surfing.

Apple here looks a lot more like her famous actress mother than her famous Coldplay frontman father ... and both of her parents have been in the news recently, thanks to a certain concert kiss cam.

But Apple's the star of the show on this occasion. Life's a beach, and she's just playing in the sand ... in her smoking hot bikini body.