The son of your great grandfather's brother was your grandfather's first cousin. That makes him your first cousin, twice removed.
Grand Uncle. Half-brother makes no difference in referencial naming of family members.
Your grandfather's brother is your Great Uncle.
Your father's brother is your uncle. Your Grandfather's brother is your great uncle. Your Great Grandfather's brother is your great great uncle.
Your grandfather's brother's granddaughter is your second cousin.
Your grandfather's uncle is your great great uncle. Your grandfather's brother would be your great uncle
Your grandfather's brother is your great uncle. Your great uncle's daughter's daughter (his granddaughter) is your second cousin.
Your grandfather's brother is your great uncle.
Your grandfather's brother is your Great Uncle.
The children of your grandfather's brother are your first cousins, once removed. You can also call them by their names.
Your father's brother is your uncle. Your Grandfather's brother is your great uncle. Your Great Grandfather's brother is your great great uncle.
Your grandfather's brother is your great uncle.
Your grandfather's half brother is your great uncle.
Your grandfather's brother's granddaughter is your second cousin.
Half-Brother.
Your grandfather's brother's grandson is your great uncle's grandson. The grandchildren of great aunts and great uncles are your second cousins.
Your grandfather's uncle is your great great uncle. Your grandfather's brother would be your great uncle
You Call your grandad's sister 'Great Aunt' and you call your grandad's brother 'Great Uncle'.
The brother of your great grandfather is your great great uncle. Your great great uncle's great grandchildren are your third cousins.