After Khloé Kardashian returned to Instagram [2] with a sweet message for Kim Kardashian, Kourtney Kardashian followed suit and wished Kim a happy birthday with a flashback photo from their teenage years. Kourtney captioned the snap, "She has been my partner for life. We always seem to end up on the craziest adventures together. I love and admire the person you have become and learn from you every day. Happy Birthday!" On the same day, Kourtney was spotted flaunting [3] her toned physique while out in LA before attending Kim's surprise bash [4] put on by Kanye West. Take a look at Kourtney's post above, then, in honor of Kim's 35th, relive her sexiest bikini moments [5]!