Your grandfather's great nephew is your second cousin.
Your grandfather's great nephew is your second cousin.
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.
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.
A great uncle is the brother of the great nephew's grandfather or grandmother.
You and your great-great-great-great-grandfather's great-great-great nephew are fourth cousins, twice removed.
Your grandfather's great nephew is your second cousin.
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 great grandfather's sister is your great great great aunt. You are her great great great nephew or her great great great niece.
Your grandfather's nephew would be your First Cousin once removed Ref: http://freepages.genealogy.rootsweb.ancestry.com/~gentutor/chart.html
Your grandfather's nephew is your parent's first cousin. Your grandfather's nephew's daughter is your second 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.