Jenner shared a slideshow of photos on Instagram, including a picture of herself dropping off Kardashian at school.
Kardashian herself welcomed her first child, daughter True, with Tristan Thompson.
"Happy birthday to my bunny @khloekardashian!! Beautiful, smart, kind and the strongest person I know, you amaze me every single day. You are truly an angel on earth, my beauty, and I am so proud of you," Jenner gushed in the caption.
"You bring laughter and love to everyone around you. You lift people up with your positivity and your passion."
"This year we celebrate you being a new mommy, and all the amazing blessings that brings. To watch you with baby True brings me the greatest joy," she added.
"I love you to the moon and back!! You deserve the world #HappyBirthdayKhloe."
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Kardashian gave birth to True in April following reports Thompson cheated during her pregnancy.
She addressed her relationship with Thompson in a tweet Monday after a fan criticized her for staying with the 27-year-old NBA star.
"You have no knowledge of what goes on in our household or the enormous rebuilding this takes to even coexist," the star wrote.
"I'm proud of my strength," she said. "I appreciate your opinion and I hope you hold that same opinion to everyone else who has stayed in situations."
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