Michael Buble "cried non-stop for four days" over the summer (11) after his beloved grandfather underwent open-heart surgery.
The Canadian crooner was devastated to learn 83-year-old Mitch needed the procedure, and was overcome with emotion as he awaited the outcome of the operation.
Michael Buble subsequently moved his grandfather into his Los Angeles home to help him recover from the surgery, and the singer is delighted with Mitch's progress.
He tells Britain's The Sun, "When grandpa was ill and could have died, I would have swapped all my record sales so he could get well. He is the reason I am a singer. He was my best friend growing up.
"Doctors said it didn't look good and he needed open-heart surgery. I cried non-stop for four days as I'm so close to him. The thought of losing him was a wake-up call.
"He's in L.A. with me, and grandma too. I am lucky that I can pay for the best doctors for him but I'm more thankful he's with me and my wife and we can see him resting and getting better."