Your great grandfather!
He would be your paternal great grandfather
Your great great grandfather.
Your grandfather's great great niece is your second cousin, once removed
The great grandson of your great grandfather's brother is your third cousin
If your great great grandfather was the brother of someone else's great great grandfather then you and that other person are fourth (4th) cousins.
Your great grandfather's nephew was your grandfather's first cousin. You are two generations removed from your grandfather and his cousin. Therefore you and your great grandfather's nephew are first cousins, twice removed.
Your great grandfather's nephew was your grandfather's first cousin. You are two generations removed from your grandfather and his cousin. Therefore you and your great grandfather's nephew are first cousins, twice removed.
The child of your great great grandfather's brother is your first cousin, three times removed.
Your great grandfather's nephew was your grandfather's first cousin. You are two generations removed from your grandfather and his cousin. Therefore you and your great grandfather's nephew are first cousins, twice removed.
If the great grandmother of A is the aunt of B's grandfather, then A and B are third cousins.
fourth cousin