Khloe Kardashian's Birthday Post For Kourtney Kardashian’s 40th Highlights Their Strong Sisterly Bond — PHOTOS

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It's no secret that the Kardashian-Jenners are a tight family. If you need further proof, check out Khloé Kardashian's 40th birthday post for Kourtney Kardashian. Khloé wished her older sister a happy birthday with such a beautiful Instagram shared on Thursday. Her post not only shined a light their close bond as sisters, but highlighted their relationship as best friends.

Next to a series of photos of the two from over the years, Khloé began her lengthy 40th birthday message by writing, "Happy birthday sweet @kourtneykardash!!! I am completely obsessed with each and everyone of my siblings. Still blows my mind how blessed we are to call each other sisters." Then, she wrote about what makes their sibling relationship that much more special. Khloé posted,

"You and I have an incredible rare bond that no matter what, it can never be broken. You’re my best friend, one of the rare few I can count on most in my life. I’m so thankful for that. I know that so many people go through life without their sister as their best friend, or without a sister in general and I don’t know how they do it. Honestly, without you my life would be boring and not as full."

The Keeping Up With the Kardashians star went onto send Kourtney positive thoughts and wishes. Khloé revealed how much her sister "deserve[s] only magical things" for the rest of her life. She concluded her birthday message by sharing, "In all of the lifetimes before and in all of the lifetimes after, I will love you! To the happiest of birthdays my sweet sister!! Jane or Suzanne (I forget who’s who) I love you!"

As KUWTK fans know, Kourtney and Khloé have long referred to one another as "Jane" for Jane Fonda and "Suzanne" for Suzanne Somers. Like Khloé expressed in a special video for Kourtney's 39th birthday, "Happy birthday Kourt! I love you so much. You will always be the Jane to my Suzanne, the Reese’s to my Pieces, the peanut butter to my jelly."

Their relationship is something to be admired. For Kourtney's 40th, Khloé also posted a bunch of photos and videos on her Instagram Story, so make sure you check those out as well.

Like her daughter, Kris Jenner also took to Instagram on April 18 to wish her eldest child a very happy birthday. It's hard for the momager to even believe that Kourtney could be 40 already. Next to a series of adorable family photos, Kris gushed,

"Happy Birthday Kourtney!!! I can’t believe you are 40!! I love you more than you can ever imagine...you will always be my baby. I am so blessed beyond words to be your Mommy and have you by my side in this precious life...you are my heart and I am eternally grateful for all of the memories that we cherish. I love you. Mommy xoxo."

You only turn 40 once, and knowing the Kardashian-Jenners, there will be some type of big celebration for Kourtney. When it comes to any type of party, the KUWTK stars always go over-the-top.

Let's hope Kourtney celebrates the right away and enjoys every single moment of her birthday with her family by her side.