"I’m so happy for you! Your baby girl is so beautiful! You are so strong, you made that look so easy! I can’t wait for our baby girls to grow up as best friends the way we are! I’m so happy I was able to return the favor of holding your leg while you pushed LOL," she wrote.
Kourtney, mom Kris Jenner and Khloe's pal Malika Haqq were also with Khloe for the birth.
It has been a rollercoaster few days for the family, who were rocked earlier this week by the release of videos purporting to show Khloe's Cleveland Cavaliers boyfriend cheating on her with several women. The close-knit clan quickly rallied and rushed to Khloe's side in Cleveland to ensure she was supported.
A source close to the family told ET on Thursday that now that the baby is born, Khloe is ready to follow her sisters back to California as soon as she can. "Right now, she realizes she needs her family around her and knows they are the people in her life that she will always love and trust," the source said.
But the drama is not dampening the enthusiasm for the new baby. Youngest sister Kylie Jenner Snapchatted the news, while momager Jenner took to Instagram on Thursday to share her thoughts on the new baby: "BLESSED!!!"