The SKIMS founder turned 43 on October 21st.

In attendance was mum Kris Jenner, sisters Khloe, Kendall, and Kylie, as well as celebrity pals such as Hailey Bieber, Kimora Lee Simmons, Steph Shepherd, Ivanka Trump, as well as many others.

However, Kim's older sister, Kourtney, was understandably missing from the fun, and not for the reasons many viewers of The Kardashians may think, given the recent spats between them on the show.

The eldest Kardashian sister is currently on 'bed rest' as she comes into the final months of her pregnancy with her fourth child, her first with husband Travis Barker.

This comes weeks after Kourtney had emergency foetal surgery that saved her baby's life, and means she had to sit out the celebrations at her sister's birthday bash.

While the due date for Kourtney and Travis' son has not been confirmed, many believe the POOSH founder could give birth anytime between now and December.

Taking to Instagram, Kim thanked her friends and family for joining her on her big day, as well as giving a special mention to her sister that couldn't make it.

"So blessed to have hit the jackpot of friends! I couldn’t have ever dreamed I would be so lucky to call these girls my friends. thank you for all the birthday love and Kourt I’m jumping in bed with you next week for our bed rest picnic," she wrote.

Kim's special shoutout to her sister seems to indicate that the tension between the sisters, as seen on this season of their reality series, has simmered.

The feud between the pair was sparked after Kim agreed to serve as the creative director for a Dolce & Gabbana (D&G) show in Milan, which Kourtney was unhappy about as D&G designed her wedding.

Things came to a head after a phone call between them at the beginning of season 4, but they have since been working to repair their relationship.

READ MORE:

Paul Mescal is a normal person as he signs up for dating app

Victoria Beckham reportedly in talks for her own tv show amid Beckham series success

Britney Spears feared family would ‘try to kill her’ during conservatorship battle