The new mama posted a special message to her younger sister, Khloé Kardashian Odom, in honor of her 29th birthday.
She also shared family photos in two collages featuring the Kardashian girls as little kids.
"Then- @khloekardashian The birthday girl! I love you so much!!!!" she wrote on the first message.
Kim followed up with another adorable set of photos and captioned the mashup, "Now- @khloekardashian The most loyal & supportive person on the planet! Ife wouldn't be the same without you Kokes!"
Kim has been resting at home with her newborn since the delivery, according to her mother, Kris Jenner.
The proud grandma also revealed that baby North is "amazing" and that both mama and daughter are "happy and healthy."
Catch a new episode of Keeping Up With the Kardashians this Sunday at 9 p.m., only on E!