Your great uncle's grandchild is your second cousin.
The grandchildren would be the parents, aunts and uncles, and first cousins once removed, of the great grandchildren.
Your great grandmother's sister is your great great aunt. Her great grandchild is your third cousin.
He would be his great great great uncle
not to be complicated , but if you have an uncle--> he has a nephew--> as you can see that's not complicated . And if you ask what is a uncles NEPHEW related to an uncles grandfather. in what way ....i would say the nephew is is the great gandfathers great grandson.
Your great grandfather's sister is your great great aunt. Her grandchild is your parent's second cousin and your second cousin, once removed.
Your uncle is your child's great uncle and your grandchild's great great uncle. Your grandson is your uncles great great nephew.
Your sister would be her great aunt and she would be your sisters great niece.
Your great grandparents brothers and sisters are your great uncles and great aunts.
Second cousins.
Your Great-Uncle is your father's uncle or your mother's uncle. Another way to look at it is to realize that your great uncle is the brother of one of your grandparents.
The common ancestor is your parents. Your children and your sister's children are first cousins. Your grandchildren and your sister's grandchildren are second cousins. Your great-grandchildren and your sister's great-grandchildren are third cousins.
your cousin