That person would be either me or my sister...if the cousin of me great uncle was my great grandfather. If the cousin was another of my great uncles, then the person would be my cousin. Example 1: My dad has a brother who is my uncle. That uncle has a father who is my great uncle. If his father or mother had sisters or brothers who had kids, these kids would be cousins to this great uncle. one of them could be my grandfather. so my grandfather's granddaughter would be me if I am a girl or my sister if I am a boy.
Example 2:
In any level of the family tree there can be cousins...children of my uncle or aunt. when they have kids they are second cousins...children of first cousins. If these second cousins have kids, they all are third cousins. So since my great uncle had a cousin which was 2 generations above me...the next generation would be second cousins and the third generation would be third cousins.
If my grandfather was not the cousin in question, then the cousin would be someone else on the same generation level, 2 levels above me and the granddaughter would be on my level and therefore my third cousin.
Your grandson and your sister's grandson are second cousins to each other.
WHAT relationship* is your Gramps to your great granddaughter? pretty tricky but (distant sisters one off)
The grandchildren of any of your great uncles and great aunts are your second cousins.
She would not be. You uncle's children are your first cousins and his grandchildren are your first cousins, once removed. Your children and your uncle's granddaughter are second cousins to each other.
An uncle's nephew and the uncle's child are first cousins to each other. The uncle's great granddaughter and the nephew are first cousins twice removed to each other.
Your granddaughter and your grandniece are second cousins or third cousins to each other
If you are a girl, your are your great aunt's cousin's granddaughter. If you are a boy, your sister is. Your great aunt also has first cousins from whom you are not descended. For those first cousins, the granddaughter is your first cousin, twice removed, or your first cousin, or your second cousin once removed, or your third cousin.
Your third cousins are the great grandchildren of your great great aunts and great great uncles.
Your great nephew and your granddaughter are second cousins to each other.
Your sister is her great grandaunt.
They would be the fourth cousins. They share a common 5 Great Grandparent.
great great (etc.) grandparents great grandparents grandparents + great uncles and great aunts parents + uncles and aunts [=parents' siblings] siblings + cousins [=uncles' and aunts' children] children + nephews and nieces [=siblings' children] grandchildren great gandchildren great great (etc.) grandhildren also cousins and second cousins [=(great-)grandparents' descendants]