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Your mother's niece is your first cousin. Your first cousin's daughter is your first cousin, once removed.
Your cousin is your Uncle/Aunt's son/daughter. Your niece is your brother/sister's daughter. So your parent's niece is your cousin.
Since your niece is your daughter's first cousin, your grand niece (the daughter of your niece) is your daughter's first cousin, once removed.
A niece. How could you not know that
cousin daughter
Your father's niece is your first cousin, and her daughter is your first cousin, once removed.
Your first cousin's niece is the daughter of her brother or sister. Your first cousin's brothers and sisters are also your first cousins. So your first cousin's niece is the daughter of your first cousin and is therefore your first cousin, once removed.
Your niece is the first cousin of your children and the first cousin, once removed, of your grandchildren.
Your father's niece is your first cousin, and her daughter is your first cousin, once removed.
Your father's niece is your 1st cousin.
For clarity, lets call your great great grandfather's niece "the niece". The relationship sequence: (1) The niece is the daughter of your great great grandfather's sibling (2) The niece is a 1st cousin of one of your great grandparents (3) The niece is a 1st cousin once removed of one of your grandparents (4) The niece is a 1st cousin twice removed of one of your parents (5) The niece is your 1st cousin three times removed
Your grandfather's niece is the first cousin of one of your parents, and your first cousin, once removed.