InstagramKourtney Kardashian's daughter, Penelope Disick, and Kim Kardashian's, North West, aren't just cousins—they're besties and even better, besties with a "secret language."
Little P celebrated her fourth birthday Friday and her Aunt Kim posted on her Instagram page the cutest video of the little girl and North, 3, dancing and singing together...not exactly in English.
"Whatever secret language u girls speak, the way you girls protect each other & love each other is so special," the Keeping Up With the Kardashians star wrote. "Penelope, North is so lucky to have a best friend like you! Happy Birthday my sweet P. I love you to the moon and back!"
Kourtney wished her daughter a happy birthday on Instagram as well, posting a photo of her little girl in a mermaid costume, similar to the one she wore at North's mermaid-themed birthday party in June.
"Happy birthday to my little mermaid!" she wrote. "Seeing the magic in the world through your eyes makes me so happy."
Kourtney's mom Kris Jenner regrammed her pic.
"The birthday girl!! #ourlittlemermaid #happybirthdaypenelope," she wrote.
She also posted another cute pic of Penelope, posing several months ago in a striped top, black skirt and sunglasses.
"Happy birthday to our little princess, my sweet angel girl Penelope!!!!" Kris wrote. "You bring so much joy to our lives and I love you more than words could ever say!! #sweetgirl #happybirthdaypenelope #myheart."
Penelope's aunt Khloe Kardashian posted on her Instagram page a photo of the two sharing a cute moment, with the reality star wearing the pastel pink wig she wore at North's bash.
"Happy birthday my sweet Penelope!!!" she wrote. "May you believe in mermaids for the rest of your life! Like your aunty does."
Penelope is Kourtney and ex Scott Disick's middle child. The two are also parents to sons Mason, 6, and Reign, 1.
Earlier this week, Kourtney and the kids enjoyed some fun in the sun and the (warmer) ocean in Miami.
The reality star posted on Snapchat a video of her little girl playing outside with a pink helium-filled balloon.