The Keeping Up With The Kardashians star is known to have a very close bond with her only brother, inviting him to live with her and now-ex-husband Lamar Odom years ago.
Khloe shared a picture of herself and Rob to Instagram today alongside a heartfelt caption.
"Happy birthday @robkardashian!!!!!! Never will I ever meet another man as great as you! I know this is the year where you will find your happiness again! I will be right by your side, holding your hand, every step of the way!!! I adore you my one and only brother!! "
Rob is the youngest child of Kris Jenner and the late Robert Kardashian Sr. His sisters are Kim, Khloe and Kourtney Kardashian, and his half-sisters are Kylie and Kendall Jenner.
While his siblings – and mum! – are always in the spotlight, Rob prefers to keep away from the cameras.
Although he appears on the show's family reality show, he rarely walks red carpets and even ducked out of attending Kim's wedding to Kanye West last year.
Rob has been in the headlines over the past year because of a struggle with his weight, which he has referenced on Twitter in the past.
Khloe wasn't the only family member sending happy thoughts his way...
"Happy Birthday to my one and only brother Robbie!!!! I remember this Vegas party of yours like it was yesterday! I love you so much and can't wait to share so many more memories with you! Kiki Riki!!!!"
"Happy birthday to my incredibly silly, wildly handsome big brother!!! @robkardashian YOU ARE MY FAVOURITE PERSON...ever! this guy is responsible for all the belly laughs I've had throughout my entire life. all the love in the world for this man."
"This was almost a decade ago but I still want to sit on ur lap like ur little sister I still am MY LOVE FOR U IS ENDLESS!!!!!! Happy birthday Robby."