Your child and your great nephew's parents would be first cousins. Their children would then be second cousins. And if they have children, they will be third cousins.
The child of your nephew is your great nephew (if a son) or your great niece (if a daughter).
Your nephew's daughter is your great niece and you are her great Aunt (or Great Uncle).Correction:Your nephew's daughter is your grand niece. You are her grand aunt or grand uncle.
She would be his Great Aunt
Your grandfather's brother is your great uncle (some would say your grand uncle). You are his great niece (if you are a girl) or his great nephew (if you are a boy).
Your nephew's son is your great nephew and you are his great aunt or great uncle.
Your nephew's son is your great nephew.
Your nephew's daughter's son is your great-great nephew. Your nephew's daughter is your great niece.
The child of your nephew is your great nephew (if a son) or your great niece (if a daughter).
Your nephew's child is your great nephew (if a boy) or great niece (if a girl). You are his or her great aunt.
Well the daughter will be your grandaughter and you will be a grandmother/grandfathther.
Your grandson and your great nephew are second cousins to each other.
Your great nephew is your kids' first cousin once removed.
Your great nephew and your granddaughter are second cousins to each other.
great nephew
Your child and your nephew are first cousins. Your child and your great nephew are first cousins, once removed.
Great Grand Nephew
Your nephew's daughter is your great niece and you are her great Aunt (or Great Uncle).Correction:Your nephew's daughter is your grand niece. You are her grand aunt or grand uncle.