Catherine shared a photo of herself and Carys from when she was very young as well as a recent photo of the 18-year-old by the beach.
"Happy 18th Birthday Carys Zeta!" the actress wrote. "You are everything, and everything is you. Thank you for the joy you bring me. At 5 am this morning, you texted me to thank me, for giving birth to you.
"That’s the kind of woman you are. Kind. Your wisdom outnumbers your years. Your beauty is deep and your heart is big enough to love and envelop the world, your sense of humour...very important... is insurmountable."
Catherine then joked, "I could go on. Your Japanese needs some work, but that’s doable. I love you angel. Mama."
Carys commented on the snap, "I love you my mamma! Thank you for all that you do."
Michael shared a photo of himself and Carys, writing, "Honey this is your Dad, wishing you the best 18th birthday any young lady could possibly have.
"You know how much I love you, how proud I am of you, and the joy I have watching you grow into the young lady you are turning out to be! Happy birthday Carys! I love you! Dad."
Carys responded, "Thank you my dadda!! I love you and thank you for everything you do. You are my biggest inspiration!"
The couple's son Dylan, 20, also shared his own birthday message for Carys, writing, "Happy 18 birthday @carys.douglas, 'Now this is not the end. But it is, perhaps the end of the beginning' — Winston Churchill. Welcome to adulthood. I love you."
Half-brother Cameron Douglas, 42, also didn't miss the opportunity to wish his younger sister a happy birthday, writing, "Happy Birthday to a remarkable young woman, sister, aunt, intellectual, and all around lovely human being.
"I could not be more proud of the person you are and the trajectory your star is travelling. Sending you all my Love baby...Enjoy your day!"
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