Sister love! Kim Kardashian took to social media on Monday, April 18, to share an adorable throwback pic in honor of Kourtney Kardashian’s 37th birthday.

“Happy Birthday @kourtneykardash Thank you for always doing everything first so I can copy you!” Kim, 35, captioned the sweet snapshot of the siblings in their preschool years, wearing identical sundresses and matching pigtails. “I don't know what I would do without you! I love you! Happy Birthday!”

As the Selfish author revealed on her website in September 2015, she still tries to emulate mother-of-three Kourt as an adult, especially when it comes to her maternity looks.

“Everyone used to say Kourtney had the best pregnancy style,” Kim said of dressing her baby bump while carrying daughter North, 2, and son Saint, 4 months, “So I would borrow a dress she wore when she was pregnant, and OMG it did not look the same!”

Kim isn’t the only member of the Kardashian-Jenner clan to send Kourtney good vibes for her big 3-7. The reality star’s momager, Kris Jenner, wished her eldest daughter a happy birthday in an equally sentimental 'gram.

"Happy Birthday tomorrow beautiful @kourtneykardash !!" Jenner, 60, wrote alongside a retro family photo. "I know it's crazy but I remember this pic like it was yesterday.. You have brought so much love, joy, and happiness into my life and I'm proud to be your Mom..”

In the picture, a young sunhat-clad Jenner holds an infant Kourtney in her arms. Standing next to the precious pair is the late Robert Kardashian, who is sporting the most fantastically '80s handlebar mustache.

"You teach all of us everyday what it means to be an amazing daughter, Mom, sister, friend, and a genuinely beautiful human being. Thank you for being such a bright light and an inspiration to me every day.." the proud Keeping Up With the Kardashians matriarch continued. "You are kind and patient and have the biggest heart and I love you more than you will ever know. You will always be my firstborn who captured my heart.... Oh, and I'm really sorry about this outfit I put you in....I love you, mommy #love #blessed #mybaby."

This is Kourtney’s first birthday since calling it quits on her 9-year romance with Scott Disick, with whom she shares kids Mason, 6, Penelope, 3, and Reign, 15 months.

"We're not getting back together right now, but I don't know what the future holds in life, in God's plan,” the E! personality said of her relationship with Disick, 32, during an April 12 appearance on the Today show. “But we're just doing our best to be the best parents. Like, he came with us to Vail and it was great. But, like, we're friends at this point.”

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