So very sorry about your gradfather. I nursed my granpa for 2 years, he too had alzheimers and even though I adored him so much, he was not the man I had known all my life during the time I cared for him.
I was heart broken when he died.....but now I think of him "upstairs" tending to the flowers....he is as I knew him as a child and not the man affected by such a horrific disease.
I am sure your granpa would have provided you with many happy childhood memeories.....treasure these for always.
Thinking of you and your family at this sad time.