"HAPPY BIRTHDAY MY BEAUTIFUL BABY LEO THAMES!" she captioned a cute shot of herself with Leo and his two-year-old big brother James, from a Vanity Fair spread. "I can't believe you are one today. My ? my miracle."
King also shared a special shout out to her son's godmother, Taylor Swift, on Twitter.
"Wow! @taylorswift13 LT's 1st bday already?!" she wrote, along with a collage of sweet pics of the "Blank Space" singer with her godson. "He sends kisses & a bangin' 2 teeth smile to his Godmother in Oz. We ? u!"
The 37-year-old actress named Swift baby Leo's godmother back in March 2015, before her son was even born, and was thrilled with her with her choice.
"It's her loving, her profound, deep…loving and caring, sharing and that’s the reason why I chose her," King told ET's Katie Krause last year. "Just how much she loves him and cares about him, and how much she cares about our family and how much I care about her, it’s a really beautiful thing," she said, before dishing that she thinks Swift would make an "amazing" mother.
Swift has been busy enjoying a whirlwind tour around Europe and the US with her new boyfriend, Tom Hiddleston. The couple is currently in Australia, where Hiddleston is set to begin filming Thor: Ragnarok.