"Her family asks for your understanding of their need for privacy at this time."
Kelly is survived by her husband John Travolta and their children: daughter Ella, 20, and nine-year-old son Benjamin.
Kelly and John's son Jett passed away when he was just 16 in 2009 following an epileptic fit.
John has also taken to Instagram to tell fans of Kelly’s tragic passing.
“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,” he wrote.
“She fought a courageous fight with the love and support of so many. 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.
The doting husband and father then apologised to followers for his foreseeable absence from the spotlight.
“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.”
John and Kelly had been married for almost three decades, celebrating their 28th wedding anniversary last September after getting engaged on New Year’s Eve in 1991 and marrying months later.
At the time Kelly shared a heartfelt love note dedicated to her husband, writing: “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.
"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," she added.