Kourtney Kardashian Wears Sultry, Body-Baring Black Dress to Her Epic 40th Birthday Bash

Helen Murphy

Ain’t no party like a Kardashian party!

The famous family pulled out all the stops for Kourtney Kardashian‘s 40th birthday on Thursday night, hosting a celebration that included a performance by Robin Thicke, a NSFW cake and even an appearance from Kourtney’s ex Younes Bendjima.

Mom Kris Jenner attended the festivities, as well as all of Kourtney’s sisters: Kylie Jenner, Kendall Jenner, Khloé Kardashian and Kim Kardashian West, who showed off the birthday girl’s look on her Instagram story.

Kourtney rocked a skintight black dress with sheer detailing, which Kim explained was “vintage Versace.” On her Instagram story, Khloé, 34, documented Kourtney’s entrance into the party as the reality star walked hand-in-hand with daughter Penelope, 6, while a saxophone player played Stevie Wonder’s “Isn’t She Lovely.”

Kim Kardashian Instagram
Khloe Kardashian Instagram

Inside the party, guests were treated to personalized Don Julio bottles and Kim, 38, pointed out that Kourtney’s bottle was engraved with her face and the hilarious caption “Most Interesting to Look At,” a reference to when Kim called her sister “the least interesting to look at.”

RELATED: Kourtney Kardashian Is 40! See Sweet Birthday Messages from Khloé Kardashian, Kris Jenner & More

The birthday cake appeared to depict a naked Kourtney sitting in a hot tub, as frosting read “Happy Birthday Kourtney!” The guest of honor was also treated to a rendition of “Happy Birthday” sung by none other than Thicke.

The biggest surprise of the night? Kourtney’s ex Bendjima appeared to be at the party, as he posted a photo on his Instagram Story of napkins that read “Happy Birthday Kourt” and shared a video that appeared to show the dance floor of the party. (Kourtney and Bendjima split in August 2018.)

Khloe Kardashian Instagram
Kim Kardashian Instagram
Kim Kardashian Instagram
Younes Bendjima Instagram

As Kourtney celebrated her 40th birthday on Thursday, a source told PEOPLE the reality star is embracing the milestone occasion and what the next year could bring.

“When she talked about turning 40 a while back, she didn’t seem too excited,” said the source. “Turning 40 is a big deal. But instead of seeing it as something negative, Kourtney turned it around and she seems very excited about her life just in general.”

RELATED: Kourtney Kardashian Is ‘Excited’ to Turn 40 and ‘in a Great Place’ with Scott Disick: Source

On Thursday, Kardashian woke up to personalized messages from her sisters and mom Kris to help kick off her birthday.

“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,” Kris, 63, captioned a slideshow of photos on Instagram. “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.”

Kim also celebrated her sister with a sweet slideshow.

“Happy Birthday @kourtneykardash I honestly can’t believe the life we have lived!” she captioned her post. “It’s such a dream to go through it all with having a sister like you by our side! You have taught me so much throughout life. You’re such an amazing mom and friend! Can’t wait to celebrate you tonight! I love you beyond what you could imagine.”

Khloé, meanwhile, gushed about the “rare bond” she shares with her eldest sister.

“Happy birthday sweet @kourtneykardash!!! I am completely obsessed with each and every one of my siblings. Still blows my mind how blessed we are to call each other sisters. You and I have an incredibly rare bond that no matter what, it can never be broken,” she wrote. “You’re my best friend, one of the rare few I can count on most in my life. I’m so thankful for that.”

She continued: “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. Today and every day, I pray that your soul is awakened and from your core, you’re happy! You deserve only magical things for the rest of your life! 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!!”