The father-of-three paid tribute to the actress on Instagram and was overwhelmed with prayers and well-wishes from fans who remembered her too.
Alongside a photo of Kelly - who tragically died of breast cancer in July 2020 - he wrote: "Happy Birthday Kelly. We miss and love you very much."
WATCH: John Travolta and daughter Ella dance in memory of Kelly Preston
His fans rushed to send tearful emojis and emotional messages of their own. One wrote: "She's celebrating with the angels," and another added: "She was so amazing," and many said she was gone too soon.
Kelly battled her diagnosis out of the public spotlight until she passed away surrounded by her loved ones, including her two remaining children, Ben and Ella.
At the time, John announced her passing and wrote: "It is with a very heavy heart that I inform you that my beautiful wife Kelly has lost her two-year battle with breast cancer. She fought a courageous fight with the love and support of so many."
John wrote a simply but poignant message on Kelly's birthday
In a candid interview with Esquire Spain, John later detailed his experience with grief as he explained every journey is "different" for someone else.
"I have learned that mourning someone, mourning, is personal," he said. "Mourning is individual and experiencing your own journey is what can lead to healing.
"This is different from someone else's journey. The most important thing you can do to help another when they are in mourning is to allow them to live it and not complicate it with yours. That's my experience."
John and his children are supporting each other through their grief
John and Kelly had been married since 1991 and shared three children together. Tragically, they lost their eldest son Jett in January 2009 at the age of just 16.
He had a history of seizures from the age of two and had to be hospitalized at 15 months with Kawasaki disease. He was also on the autistic spectrum. Jett died during a Christmas family holiday in the Bahamas.
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