The actress -- who is married to the celebrated star's 75-year-old son, Michael Douglas -- has been close with her father-in-law since she and Michael tied the knot in November 2000, frequently sharing sweet photos and tributes to the iconic actor on social media.
In remembering Kirk on Wednesday, Catherine posted a sweet black and white photo of her kissing her father-in-law on the cheek. "To my darling Kirk, I shall love you for the rest of my life. I miss you already. Sleep tight..." she captioned the pic.
Following his death, Michael confirmed the news of his passing and paid tribute to his father in a heartfelt tribute on social media.
"It is with tremendous sadness that my brothers and I announce that Kirk Douglas left us today at the age of 103," he wrote, in part. "To the world, he was a legend, an actor from the golden age of movies who lived well into his golden years, a humanitarian whose commitment to justice and the causes he believed in set a standard for all of us to aspire to. But to me and my brothers Joel and Peter he was simply Dad, to Catherine, a wonderful father-in-law, to his grandchildren and great-grandchild their loving grandfather, and to his wife Anne, a wonderful husband."