How Caitlyn Jenner Welcomed Kylie Jenner's Baby Into the World
Inside Kylie Jenner's Secret Pregnancy

"My daughter just had a daughter," Caitlyn says of Kylie's new arrival.

Caitlyn Jenner is thrilled to have another grandkid.

The reality TV star celebrated Kylie Jenner giving birth to a baby girl by sharing a message to her daughter on Instagram late Monday afternoon. The comments, posted alongside a baby photo of Kylie, are her first on the birth.

"My daughter just had a daughter," Caitlyn wrote. "It's amazing to be by your side through this journey. She's SO beautiful already. Can't wait to watch her grow."

Caitlyn's words come as others in the Kardashian-Jenner clan have started to speak out about the family's newest member and Kylie's new gig as mom.

"She's amazing. An amazing mom," Kris Jenner told PEOPLE on Monday night. "Any mom just wants her family to be happy, healthy, peaceful, joyful and that's my joy. They're my heart!"

She also said the video Kylie shared about her pregnancy journey had her "bawling." "I was crying so hard, especially at the end. And I still cried," added Jenner.

Kylie also revealed some of the gifts she got from her family members on Snapchat, including floral arrangements from Kim Kardashian and Kanye West, Kourtney Kardsahian, Khloe Kardashian and BFF Jordyn Woods. Brother Rob Kardashian also sent "Happy Birthday" balloons for his niece. But baby daddy Travis Scott outdid them all, sending her 443 roses in honor of their daughter's birth time.

Kim shared an additional message to Jenner on her official website, writing: "Mommy Kylie!!! You did it!!! I'm so incredibly proud of the woman you have grown up to be and I know that you are going to be the best mom to your new baby girl! Our girls are two weeks apart and I can’t wait for them to be besties! I am so proud that you do what you want to do and live your life the way you want, you will pass down all of those amazing qualities to your baby girl. You were made to be a mom! I love you!"

Khloe also celebrated her sister with an Instagram photo showing their baby bumps side by side.