How do I contest a deed

My mother died last week, March 9th. My father died 2 years ago. For 40 years they had a will leaving everything to my brother and I equally. My brother and I shared care of my mother in the last 2 years. When it was his turn in December, I have just found out that he had her deed her two properties over to him as a gift. He says that she also had a new will made leaving everything to him. It has yet to be probated. I only have a copy of the old will. On my mother;s death certificate it states that she had dementia. Since the deeds were gifted only 3 months ago, do I have any legal ground to contest this ?

You certainly do--that is very odd and if she had dementia the court may very well void any last minute will...you indeed may contest that.