An extremely different family problem.

[Sometimes Steffi]

First, your child is only 3 years old. At this point he doesn't even know what he likes and dislikes. He is exploring and hunting for his identity. I personally feel that you handled well. So what if grandpa doesn't like it. He is not grandpa's child. He is your child and you will raise him as you see fit as long as you are not violating the law.

There are a number of trans girls who new at 3 or younger, and I've even met some. They were probably trans even earlier, but didn't know how to verbalize it.

Let it play out, but you should take it as an early warning.