Kardashian, 29, penned a note on her website congratulating sister Kourtney and Scott Disick on the recent birth of their son, Mason.
"I'm sure you guys already know, but I wanted to do a quick post to congratulate Kourtney and Scott on the birth of their son Mason Dash Disick," Kim wrote Wednesday. "The whole family is so thrilled, excited and blessed to have Mason in our lives and we couldn't have asked for a more perfect gift this Christmas!"
The "Keeping Up with the Kardashians" star also gushed about how excited her family is to welcome a new addition.
"Khloe, Kendall, Kylie and I are officially auntie's (sic), Rob is an uncle, Bruce is a grandpa... and, well... mom is a grandma, and as much as she might say she doesn't like being called one, we know she secretly loves it!!" Kim joked.