Rob Kardashian shares rare social media post for sister Khloé's birthday: 'So thankful'

Rob Kardashian shared a rare heartfelt tribute to sister Khloé for her birthday Tuesday.

The youngest Kardashian has tended to shy away from the reality TV spotlight, but he posted a social media message in honor of Khloe turning 39.

"Wishing you nothing but good health and happiness forever my darling buttercup !" he wrote in an Instagram post Tuesday. "I love you so much and so thankful to have u in my life and for all that U do for Dream and I. I don’t know what I would do without you."

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"My favorite human being in the world. You’re my heart beat," Khloé replied to her brother in a comment.

Kris Jenner, Kourtney Kardashian honor Khloé Kardashian for her birthday

Other family members shared in the love for Khloé on her special day.

"Happy birthday to my beautiful bunny @khloekardashian!!!! Khloé you are the sunshine of my life,” mother Kris Jenner said on Instagram. Jenner shared a nostalgic video with footage of Kardashian as a child alongside the emotional tribute.

“You are the most amazing daughter, mommy, sister, auntie, best friend, neighbor, and such a huge part of my heart!!!!!" Jenner went on. "You are so smart, strong, talented, beautiful inside and out, kind, sweet, thoughtful, creative, funny, and witty."

"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. I love you more than you will ever know and I cherish and treasure every single moment we get to spend together," she concluded. Jenner also added a reference to the Stevie Wonder song "You Are the Sunshine of My Life."

Kourtney Kardashian also used a Stevie Wonder song to celebrate her sister, posting an Instagram story with a clip of the artist's song "I Just Called to Say I Love You" playing in her car. "It's @khloekardashian day!!" she wrote, calling her sister an "angel."

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This article originally appeared on USA TODAY: Khloe Kardashian gets rare birthday tribute from Rob Kardashian