The model turned 32 on Sunday, just four weeks after delivering the couple’s first child, son William “Billy” Christopher, whom they named after the actor’s late father William “Bill” Stamos.
In celebration, Stamos shared a photo of the new mom and their baby boy sharing a cuddle in bed, writing in the touching caption, “#HappyFirstMothersDay/Birthday! As if it were even possible, when you became a mother, you became even more beautiful.”
“You’ve brought more love and joy to my life than I ever imagined,” added the 54-year-old star. “Thank you from the luckiest guy on the planet. XOJS”
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Caitlin shared her own gratitude for her husband on Sunday via a heartwarming photograph of the actor and little Billy, showing the newborn asleep on his dad’s chest.
“So much love for my boys, thank you for making me a mommy ❤ 🤱🏽,” she wrote to accompany the image. “I’m the luckiest birthday girl in the world to spend today with you two.”
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Ten days after his son’s arrival, Stamos admitted to PEOPLE that the first week and a half of fatherhood has been a very emotional time for him.
“I cry a lot,” said the first-time father, who wed Caitlin in February. “It’s more beautiful than anyone told me it would be. I’ve been waiting a long time.”
And some of those tears were triggered by song. “I woke up this morning, and I sang him ‘House at Pooh Corner’ ” revealed Stamos, breaking into the 1971 Kenny Loggins tune and its “Christopher Robin” lyrics. “His middle name is Christopher.”