Olivia Newton-John also discussed her ongoing friendship with John Travolta who played the Danny Zuko to her Sandy Olsson in the 1978 Grease film.
"He's a dear friend and he always will be," Olivia said.
"We formed great bonds making that film as you can imagine and it's always amazing to me that it's 40 years now and every 10 years I've thought 'Oh it's going to fade away now' but it just gets bigger and bigger."
She added: "It seems to find a younger audience all the time, it's really quite amazing."
When news broke of Kelly's passing, Olivia shared a touching tribute to her friend via Instagram with a throwback photo of the pair.
"@therealkellypreston was a radiant, warm and gentle spirit - a loving, devoted wife, mother and sweet friend," she penned.
"My heart breaks for John, Ella and Ben. No words can express my sorrow for her family. Kelly’s light shines on in her beautiful children. Xox"
The Travolta family was rocked by more tragedy just three months after Kelly's passing when John's nephew Sam (the son of John's brother Sam Travolta Sr) died aged 52.
ONJ recently shared her personal story of the "overwhelming" moment she was diagnosed with cancer in a video for the new Olivia Newton-John Foundation, which aims to help cancer survivors.
"I am probably one of those people who is living beyond cancer, living beyond probably what people expected to happen," she explained in the clip.
"I knew immediately something was wrong.
"I had a mammogram. The mammogram was benign and I had a needle biopsy that was also benign," she added. "I don't say this to scare women, but you have to just trust your instincts."