A representative of the family told PEOPLE exclusively that Preston died following a two-year battle with breast cancer.
"Choosing to keep her fight private, she had been undergoing medical treatment for some time, supported by her closest family and friends," the family representative said. "She was a bright, beautiful and loving soul who cared deeply about others and who brought life to everything she touched. Her family asks for your understanding of their need for privacy at this time."
Preston is survived by her husband, 66, and their children: daughter Ella, 20, and 9-year-old son Benjamin. Son Jett died at age 16 in January 2009.
"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," Travolta shared on Instagram.
"My family and I will forever be grateful to her doctors and nurses at MD Anderson Cancer Center, all the medical centers that have helped, as well as her many friends and loved ones who have been by her side. Kelly's love and life will always be remembered," the actor wrote.
"I will be taking some time to be there for my children who have lost their mother, so forgive me in advance if you don't hear from us for a while. But please know that I will feel your outpouring of love in the weeks and months ahead as we heal," he concluded.
In September 2019, Travolta and Preston celebrated their 28th wedding anniversary. "Happy Anniversary to my wonderful wife ♥️ @therealkellypreston," the Grease actor wrote on Instagram at the time.
"To my dearest Johnny, the most wonderful man I know. You have given me hope when I have felt lost, loved me patiently and unconditionally… made me laugh harder than any other human being possible… shared the most beautiful highs and at times low," the mother of three shared in her heartfelt tribute to Travolta. "You're a dream Daddio and make life so much fun!! I trust my love with you implicitly… with you I know I will always be okay no matter what happens… I love you forever and completely. Happy 28th Anniversary @johntravolta."
The couple met in 1987 while filming The Experts. After dating briefly, Travolta proposed at the Palace Hotel restaurant in Gstaad, Switzerland, on New Year's Eve 1991. When they got married on Sept. 5, 1991, Preston was two months pregnant with their son Jett.
Preston's final Instagram post was a family selfie in celebration of Father's Day in June. "Happy Father’s Day to the best one I know, we love you," she captioned the photo which starred their son Ben and daughter Ella. In addition, Preston posted a black-and-white portrait of Travolta and Jett.
The actress' final film role was in the 2018 film Gotti in which she played Victoria Gotti, the wife of Mafia boss John Gotti, who was portrayed on screen by Travolta.