'This is 40!': shows off incredible bikini body while on a ...

has shared her first photos to Instagram from her secret 40th birthday vacation. 

On Monday morning the Keeping Up With The Kardashians star posted three images while in the ocean on a white sandy beach. It has been reported she was at a private island in the Caribbean with her friends and family for a big celebration.

The mogul looked sensational in a nude string bikini that made the most of her sizzling hourglass shape as she added, 'This is 40!'

Still a hot thing: Kim Kardashian has shared her first photos from her secret 40th birthday vacation to Instagram

Still a hot thing:  has shared her first photos from her secret 40th birthday vacation to Instagram

Kim had on a very small nude string bikini with mirrored wraparound sunglasses and a Louis Vuitton scarf on her head as she went knee deep in the crystal light blue waters on a white sand beach. Her nails were painted electric yellow.

The Kourtney & Kim Take Miami veteran wore her long dark hair down to her bottom as she added a yellow gold ID bracelet. 

The star turned 40-years-old on October 22.

The mother-of-four - she has North, Saint, Chicago and Psalm with Kanye West - did not have a big party in Los Angeles, but rather had a small get together ahead of time with her family for an E! special about her life.

Khloe, Kourtney, Kylie and Kendall were all there and even danced for her while in black outfits. 

Heating up the tropics: On Monday morning the Keeping Up With The Kardashians star posted three images while in the ocean on a white sandy beach. It has been reported she was at a private island in the Caribbean with her friends and family

Heating up the tropics: On Monday morning the Keeping Up With The Kardashians star posted three images while in the ocean on a white sandy beach. It has been reported she was at a private island in the Caribbean with her friends and family

The KKW Fragrance CEO saved all the fun last week for a getaway with those closest to her.

According to PageSix, she flew some of her closest friends and relatives out to a private island to mark her milestone birthday.

But because Kim did not tag her location in her new Instagram photos, it cannot be known for sure where she is. 

'All the guests know is when to be ready to be picked up for the flight, which will leave the Los Angeles area early next week,' a source told the outlet last week.

40 sure looks good on her: The beauty mogul looked sensational in a nude string bikini that made the most of her sizzling hourglass shape as she added, 'This is 40!'

40 sure looks good on her: The mogul looked sensational in a nude string bikini that made the most of her sizzling hourglass shape as she added, 'This is 40!'

'The destination is being kept strictly under wraps for privacy

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