North West Promises Kim Kardashian She'll Never Grow Up in Adorable Video

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North West turned three on Wednesday and her mother already thinks she's growing up too fast.

"She promised me she wouldn't get any bigger," Kim Kardashian West captioned an Instagram video of her daughter, who was wearing a PilyQ swimsuit. "I can't believe my baby girl is three years old today!!!! Northie, I love you so much. I can't even explain it! Happy Birthday to my favorite mermaid!!!

WATCH: Kim Kardashian Face Swapping With North West Is Mesmerizing

North's grandmother, Kris Jenner, also shared the video with a super sweet message. "Happy third birthday to my little angel, my precious granddaughter North!!!" the 60-year-old momager wrote. "I can’t believe you’re three today! You are growing into the most beautiful little girl!!! You bring us so much joy and I thank God every day for blessing us with you. I love you beyond words!"

WATCH: This Might Be the Best Photo of North West of All Time

Khloe also posted a pic in celebration of her niece's birthday. "Happy birthday Northie! My baby! My heart! KoKo Loco loves you!" she wrote.

Meanwhile, Kim went on to post a message for North on her website, along with some precious photos. "The joy of my world, my best friend -- I would be lost without you," the 35-year-old reality star wrote. "I've loved seeing you grow up, and I can't wait for many more amazing years. I love you, my bubs!"

North is definitely her mother's muse, and is frequently featured on Kim's Snapchat and Instagram. Check out some of the stylish toddler's most adorable moments above.

WATCH: North West Adorably Throws Shade at Kim Kardashian's Lip Syncing