Kourtney Kardashian celebrated Kim Kardashian's 45th birthday with a heartfelt throwback post that had fans swooning.

The Lemme founder shared a carousel of nostalgic photos on Instagram."Best friends forever," Kourtney wrote in the caption.

The first snap showed the two striking a pose back-to-back in matching bob cuts, giving off major '90s vibes. Another picture featured the sisters in cozy robes, their faces covered in what looked like a homemade face mask.



Source: @kourtneykardash/Instagram

Source: @kourtneykardash/InstagramThe sisters wore tiny bikinis in a tropical vacation photo.



But the post took a sultrier turn when Kourtney included a sun-soaked bikini photo that instantly stole the show. The reality stars were seen lounging by the water in barely-there swimsuits during a tropical getaway. Kim stunned in a tan-patterned two-piece that hugged her curves, while Kourtney sizzled in a red string bikini that left little to the imagination. Both rocked sleek sunglasses as they posed under the sun.



Source: @kourtneykardash/InstagramKourtney Kardashian shared a throwback post to celebrate Kim Kardashian's 45th birthday.



Khloé Kardashian also joined in on the birthday love, sharing a heartfelt tribute to her big sister on Instagram. "Happy Birthday to my sister, my best friend, my forever twin flame in chaos and greatness, @kimkardashian where you go, I go," she began her post.

Khloé continued, "Every year, I'm in awe of how you continue to evolve. Somehow, you keep leveling up in strength, grace, wisdom, and heart. You've always been powerful, but lately it feels like you've tapped into an even deeper layer of yourself, calmer yet more unstoppable, grounded yet still dreaming bigger than ever."



Source: @khloekardashian/Instagram

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She wrapped up her message by calling Kim her "ride-or-die," writing, "You and me forever, kiddo.

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Source: MEGAKhloé Kardashian wrote a touching birthday tribute for her sister.



Meanwhile, Kim celebrated her big day across the globe - bringing her signature Hollywood glam to Paris. The SKIMS mogul hit the pink carpet for the All's Fair premiere, turning heads in a powder-blue vintage Dior gown by John Galliano from the Spring/Summer 2000 collection. The off-the-shoulder satin dress featured a plunging neckline and zip-up bodice that showed off her world-famous curves.



Source: MEGAKim Kardashian celebrated her big day in Paris at the 'All's Fair' premiere with her mother, Kris Jenner.



Keeping things chic, Kim styled her hair in a tight ponytail and went for her signature soft-glam look - a glossy nude lip, bronzed glow and diamond accessories that sparkled under the lights.

Her Paris appearance also doubled as a mini birthday celebration, as her mom, Kris Jenner, and All's Fair castmates joined her on the carpet. Kris stunned in a 1993 black ruffled Oscar de la Renta gown, pairing it with jewelry from Lorraine Schwartz and Van Cleef & Arpels.

According to the show's synopsis, All's Fair follows a group of powerhouse female divorce attorneys who break away from a male-dominated firm to start their own practice. "They navigate high-stakes breakups, scandalous secrets and shifting allegiances - both in the courtroom and within their own ranks," the description reads.

Directed by Ryan Murphy, All's Fair will begin streaming on Hulu starting November 4.