The reclusive reality star shared a sweet post to commemorate his sister's special day.
Rob, 36, made his rare return to Instagram to share a pair of photos -- including one of himself and the birthday girl.
"Happy Birthday @khloekardashian 🎈🎈🎈🎈🎈" Rob wrote in the caption. "Wishing you nothing but good health and happiness forever my darling buttercup!"
"I love you so much and so thankful to have u in my life and for all that U do for Dream," he added. "I don’t know what I would do without you 🤞🤞🤞💙😍💘💘🍹🍹😛🏄♂️🍻🥵🥰🏆🧚♀️🦈🎾💪😈 happy birthday 🎈🎁🎂🎉"
Meanwhile, Khloe's sister, Kourtney Kardashian, also honored the Good American founder's special day, sharing some key throwback photos to her Instagram Story.
One post showed Khloe looking stunning in an elegant white dress -- which Kourtney, 44, captioned, "An angel" -- and another was a promo poster for their old reality docuseries, Kourtney & Khloe Take Miami.
"Happy birthday to the love of my life !!!!! i couldn’t do it without you @khloekardashian," Kylie captioned the pics. "You mean the whole world to me. i love you forever and beyond."
Khloe's mom, Kris Jenner, took to Instagram as well to share a touching tribute to her daughter. The family matriarch shared a heartwarming video montage made up of home movies from when Khloe was a toddler, set to Stevie Wonder's "You Are the Sunshine of My Life."
"Happy birthday to my beautiful bunny @khloekardashian!!!! Khloé you are the sunshine of my life… You are the most amazing daughter, mommy, sister, auntie, best friend, neighbor, and such a huge part of my heart!!!!!" Kris wrote. "You are so smart, strong, talented, beautiful inside and out, kind, sweet, thoughtful, creative, funny, and witty. You are the best chef, best party planner, best organizer, and you are the auntie and mommy that everyone wants to be with!!! You are the one that celebrates all of us. You are the best and most incredible cheerleader to everyone!! You are the life of every party!!!"
"I thank God every day for the blessing of being chosen to be your mommy," she added. "I love you more than you will ever know and I cherish and treasure every single moment we get to spend together. Mommy xo ❤️🥰😍🎂🥳🙏🏼"