You're a Great Aunt to your nephew's son, who is your great nephew.
You are your nephew's uncle, or aunt, and his son's great uncle, or great aunt. Your nephew's son is your great nephew.
Your niece's son is your great nephew. You are his great aunt or great uncle.
a nephew's kid to his aunt's kids would be their cousin.
Your brother's (or your sister's) son is your nephew and you are his aunt if you are a female or his uncle if you are a male.
You would be his great aunt. To you he would be your great nephew.
Your nephew's son is your great nephew and you are his great aunt or great uncle.
A nephew is a cousin to his aunt's son.
Your nephew's son is your grand nephew or, some would say, your great nephew. You are his great aunt or great uncle.
Your nephew's son isyour great nephew. You are his great aunt or great uncle.
Your nephew's grand son is your great great nephew and you are his great great uncle (or aunt)
Your niece's son is your grand nephew, and you are his great aunt.