The 17-year-old reality star celebrated her elder sister on the US holiday with a cute Instagram collage of pictures and a lovely caption that had fans going, 'awww!'
Kylie wrote: "Thank you for being you and being another mother figure to me my whole life and doing the same for our nieces and nephews. Whoever one day gets to have you for a mum will be the luckiest in the world. To the ones who've tried and haven't received, I celebrate you on this day too."
Across her picture collage was the message: "Don't forget about your first daughter when you decide to start your own family."
Nearly one million people have 'liked' the post so far with comments including: "So sweet. Beautiful heart and beautiful girl."
Kylie has often spoken about her close relationship with Khloe, saying at one stage Khloe was sometimes more of a mother to her than her actual mum Kris Jenner.
Back on Khloe's 29th birthday in 2013, Kylie and Kendall shared a sweet message for their "second mum" online:
"Happy Birthday to our amazing sister and second mother Khloe Kardashian!!! We love you with all our hearts and can't thank you enough for all your love and support throughout the years! You have truly been an inspiration to us our entire lives. Can't wait to celebrate your birthday Khlo! Xoxo Kendall and Kylie".
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