Grandfather Grandfather

I have been givin the chance to contact my grandfather. I can't even remember the last time I saw him. It has been at least 7 years. So much has happened since then. Goodness, he doesn't even know he is a Great-Grand. Much less that I even graduated highschool, he doesn't even know I attended.

Some background....

He is biologically my step-grandfather, but has always been Grandpa to me. Where there has been ill feelings with other family members, he has always been nice to me, my brothers and my mum. One of my fondest memories of him, was when we all lived together. I remember him playing with us and laughing with us all the time. Later I was told he even played with us after he had arm surgery and wasn't supposed to lift us. He had gotten in a bad accident and the muscles in his arm was torn apart, they had to replace it with some leg muscles. However, he slipped out of our lives when my grandparents on my dad's side got divorced. I tried to get his address out of my dad to invite him to my graduation but I was given a stern no and that was that.

But now I have it in my hands. I have no clue where to start my letter. He meant alot to me and its hard to just pick up and act like nothing happened, although i'm sure he would understand i was a child and had no say in the matter. So still what do I say?