I am so sorry to hear this, this happen a few year ago to our family no only once but twice my grand father inlaw past away first and then a few years later his wife my grand mother in law passed. It was hard but being they were both in their 90's I could only feel that God wanted them to be with him during the season when Heaven is at it's best. Plus Granny's birthday was only a few days later and she would have wanted to be with grandad on her birthday, they had been married for over 65 years. Just think of it this way. He is in Heaven with the Angels looking down watching you have a wonderful Chirstmas and wanting you to celebrate. Make it extra special for his memory.
I remember my grandfather saying we should celebrate when someone pass into Heaven, they are nolonger in pain or have worries and cry when a child is born. I will keep you in my thoughts an prayers.