I'm so Sorry for your loss.
My Grandparents on my mom's side died before I was Born.
But, my dad lost his mother about 2 years ago. Even though I never knew her, like you I feel more sorry for my dad.
My Dad was very upset. About a week after the Funeral he came up to me and said:
"Aaron. Losing someone taught me to hold the people that love you close, and to never forget to tell them you love them as well. Because you never know when something might happen to them, or to you as well.
You must cherish each and every day together, never go to bed angry, and never be afraid to show somebody you care."
I hope Tomorrow brings a better and brighter day for you.