Kim Kardashian slammed for 'outshining' Kourtney in bikini photo - but it backfires

Kourtney Kardashian turned 45 years old on Thursday. And to celebrate her day, Kim Kardashian took a moment away from promoting the news SKIMS app and wished her sister a happy birthday.

The SKIMS founder posted a picture of herself, Khloe and Kourtney from their vacation in Turks & Caicos. The three are seen posing on the beach, wearing black bikinis and showing off their iconic figures.

In the caption, Kim reminisced on their memories of watching their own children enjoy the things they did when they were younger. She wrote: "Happy Birthday Queen @kourtneykardash There’s no one on this planet that I have spent more time with and have all of the same memories with growing up than you and I cherish them all. Sharing a room and friends and cars and our lives together for four decades has been the most magical journey to have you by my side."

READ MORE: Kim Kardashian's real swimsuit size revealed as SKIMS makes majors blunder

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She continued to write: "I love you and I can’t wait for another 45 years together! I will especially cherish this last sister trip where all of our kids had dance parties til they passed out, the way we all did growing up! Celebrating you today and grateful to you forever for always giving the best advice a sister could possibly give!"

Even though the caption was heartfelt and seemed genuine, fans came after the star, cynically believing that Kim only posted that photo because she "looked good." One person in the comments wrote: "Now you know she’s not going to like this photo… lol it’s her bday Kim.. lol." Another person wrote: "Kim knew what she was doing lmao." A third person wrote: "Of course she would post a picture where she looks good and outshines Kourt." A user even thinks the two are feuding and believes this was "intentional" to make Kourtney look bad.

Kourtney stans came at her defense and praised her natural postpartum figure. One person wrote: "Kourt looks so fire postpartum!!!" Another person: "Jokes on Kim cause I actually think Kourtney looks the best here… most natural." A third person wrote: "I don’t know what everyone is on about Kourtney looks GREAT ! I don’t even look like that and I didn’t have a baby a few months ago."

Kourtney did not think too much about it as she commented on the post and expressed her love. She wrote: "This caption. I love you sooooo and so grateful for all of the incredible memories we have together… when I think it, it’s like a movie plays in my head of all of them! So blessed!"