John - who shared three children with his late wife - appeared on Kevin Hart's talk show series Hart to Heart when he spoke about the aftermath of their loss.
WATCH: John Travolta shares rare video with son ahead of anniversary of Kelly Preston's death
"He said to me once, 'Because mom passed away. I'm afraid you're going to'," John, 67, said of ten-year-old Benjamin.
"I said, 'Well, it's a very different thing.' And I went through the differences about my longevity and her limited life," the Face/Off star continued.
John pictured with his children, Ella and Benjamin
"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.'
"'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.'"
Jett Travolta tragically died when he was just 16
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 hospitalised at 15 months with Kawasaki disease. He was also on the autistic spectrum. Jett died during a Christmas family holiday in the Bahamas.
John and Kelly had been married since 1991
Actress Kelly was only 57 when she passed away. In a statement at the time, her devastated husband said: "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."
Read more HELLO! US stories here