For the Disneyland day-out, she opted to go make-up free in a baggy black sweatshirt and blue jeans.
It's no surprise the reality tv staar has become more confident in recent years as she has upped her training regime and now trains almost every day with her sister Khloe and is a famously clean eater who avoids dairy and sugar.
The reality star's impressive rear was impossible to miss in a nipple-baring snap, which she shared with her 56 million followers.
The big sister of Kim, Khloe, et al looked jaw dropping as she gave an almighty hair flick as she stood naked in a dimly lit pool. I don't know what I would do without you! "I love how close we were growing up - and still are today".
Of course, Kourtney's mother, Kris Jenner, also shared something. The Keeping Up With the Kardashians star took to Instagram on Tuesday morning to unleash the wildly steamy photo that leaves nothing to the imagination. "You bring happiness love and light and are such an inspiration to me, and everyone around you", the 61-year-old momager wrote.
Just two years shy of turning 40, Kardashian took the opportunity to prove that she still possesses a body that everyone from Justin Bieber to Scott Disick yearns to touch. "You are such an incredible mother, sister, friend, and daughter and I love you more than words can ever say.... you are handsome inside and out my sweet girl, have an awesome day, mommy xoxo #love #family #grateful #happybirthdaykourtney". "You are such an incredible mother, sister, friend, and daughter and I love you more than words can ever say. you are lovely inside and out my sweet girl, have an awesome day, mommy xoxo #love #family #grateful #happybirthdaykourtney".
Meanwhile, youngest sister Khloe, 32, also shared a montage of newer clips of the duo, writing, 'Happy birthday to the Milly to my Vanilli'. Kim Kardashian was among the first to wish her sister, followed by Khloé Kardashian.