This question is unanswerable. To explain the "relationship between" you must specify two things. Only one, "grandfather's brother's great granddaughter" is specified.
If the question were about the relationship between you and your grandfather's brother's great granddaughter, the answer would be that you are second cousins, once removed
He or she would be your forth cousin.
second cousin once removed
Your grandfather's first cousin's grandchildren are your third cousins.
First cousin twice removed. A first cousin would be your cousin's child. Twice removed means that you are two generations apart.
You are third cousins.
Your grandmother's first cousin's grandson is your third cousin.
Your great grandmother's first cousin is your first cousin three times removed.
Your grandmother's first cousin is your first cousin twice removed. Your grandmother's second cousin is your second cousin twice removed. And so forth.
Your third cousin.
Your great grandmother's first cousin's grandson is your third cousin once removed
The children of your grandmother's first cousin are your second cousins, once removed.
You and your first cousins share the same Grandmother.
The first cousin of your great great great grandmother is your first cousin, five times removed.
Your grandmother's nephew is first cousin to one of your parents, and is therefore your first cousin once removed.
It would technically be considered your half- cousin since you do have the same grandmother but a different grandfather.
Your grandmother is first cousins with cousin. Your parent would be the second cousin of the cousin's son. That would make you second cousins once removed.
Your grandmother's first cousin is your first cousin, twice removed. Your grandmother's second cousin is your second cousin, twice removed.