On Wednesday -- which would have been Preston's 59th birthday -- the 67-year-old actor posted a photo of her to his Instagram and wrote a caption that said, "Happy Birthday Kelly. We miss and love you very much."
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Preston passed away in July 2020 after a two-year battle with breast cancer which she and her family kept private. She left behind her husband, as well as son Benjamin, 10, and daughter Ella, 21. Preston and Travolta also shared son Jett, who died in 2009 at the age of 16.
Since her death, the "Hairspray" actor has frequently posted tributes to Preston on social media.
He featured Preston back in May and wished the actress a Happy Mother’s Day, marking the first one since her passing.
"Dearest Kelly, you brought into my life three of the most wonderful children I have ever known," he wrote at the time. "Thank you. We love and miss you. Happy Mother's Day."
In an interview with Esquire Mexico in April 2021, Travolta also opened up about his grieving process and his outlook on death after losing both his wife and son.
"Grief is personal and finding your own path is what could lead to healing. It's different than someone else's journey," he stated. "The most important thing you can do to help people going through grief is allow them the space to live it and not complicate their journey with your own."
The actor also made a recent appearance on Kevin Hart's series on Peacock called "Hart to Heart," where he shared his son Ben started to fear Travolta's death after losing Preston.
"I said, 'Well, it's a very different thing.' And I went through the differences about my longevity and her limited life," Travolta told the comedian. "I said, 'But you know, Ben … you always love the truth and I'm going to tell you the truth about life. Nobody knows when they're gonna go or when they're going to stay.'"
He concluded, "Your brother [Jett] left at 16. Too young. Your mother left at 57. That was too young. But who's to say? I could die tomorrow. You could. Anybody can," he added. "So let's look at it like it's part of life. You don't know exactly. You just do your best at trying to live the longest you can."