My Grandfather Died

I got a phone call this afternoon from my mother that my grandfather had just died.
It was very shocking, as he had not been in the hospital or sick. Granted he was 91, going on 92, but his doctors made it sound like he had years and years ahead of him.
He had some sort of attack in the hallway of the assisted living home where he was living, nobody knows whether it was a heart attack or stroke. My mother had just dropped him off from taking him to the eye doctor.
Apparently the last thing he did before dying was buy and sign my birthday card.
I'll be cancelling my birthday party, which was set for Friday, and instead I'll be flying to Dallas Thursday, the day after tomorrow. I didn't think I'd be back there so soon.
A little background in that my grandparents helped raise me and I was very close to them. My grandmother died a few years ago after a long painful battle with Alzheimer's.
I had meant to call my grandfather this week, as my birthday was coming up. I just kept saying that to my mother over and over again on the phone - I meant to call him this week.