In an intimate social media post, Kardashian – who is 7 months along in her own pregnancy – shared a heartfelt message to her baby sister.
"Congratulations My Sweet Kylie! What a magical ride it's been! I'll miss you bumping along with me. Never in a million years did I think we would do this together but it's been that much more special because of it. God is so great!! He had His plan all along! I love you little mama 💕 love big mama."
Kardashian accompanied the adorable tribute with a never before-seen-picture of the two sisters donning their baby bumps in crop-tops.
Jenner's baby announcement came after months of speculation about the Keeping Up With The Kardashians' star's pregnancy.
Taking to Instagram, the 20-year-old confirmed "beautiful and healthy baby girl" was born on February 1, 2018.
Jenner apologised for keeping fans 'in the dark" throughout her pregnancy but explained that she chose to keep it private to stay healthy and stress-free.
The star also shared a video of her pregnancy journey with her 101million Instagram followers.
In the video, her best friend Jordyn Woods explains how Jenner discovered her baby news.
"She took a little test... and then she passed it to me... I was surprised, " Jordyn says before footage of Kylie's ultrasound is shown.
The video shows intimate details of Kylie's pregnancy, including her first official baby bump photos, her baby shower and the moment Kylie gives birth to her baby girl.
Watch a snippet below.
Or watch the whole emotional footage below.