Well either you had a child with your sibling or with your spouse's sibling.
The daughter of a person's brother or sister is that person's Niece The son of a person's brother or sister is that person's nephew
Your nephew's son is your great nephew. Your niece's son is also your great nephew.
The person is your nephew :)
A great great grandchild and a great great nephew of the same person are third cousins, once removed.
Your nephew's son is your grand nephew or great nephew.
Your nephew's son is your great nephew.
Your nephew's son is your great nephew.
the son of the person who has died and if they have no son, a close nephew.
It is your sister's or brother's son, your adopted sister's or brother's son or your half sister's or brother's son. That would make you an aunt or uncle.
Your wife's nephew is your nephew and his son is your wife's, and your, great nephew.
If your sister had a son, then he is your 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.