The son of your great grandfather's brother was your grandfather's first cousin. That makes him your first cousin, twice removed.
Your grandfather's brother is your 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.
Oh, dude, you call your great grandfather's brother your "great great uncle." Yeah, it's like the great granddaddy of uncles or something. So, if you ever run into him at a family reunion, you can be like, "Hey, what's up, great great uncle?" and he'll probably be like, "Who are you again?"
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 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.
Your grandfather's half brother is you great uncle. Some would insist on calling him your half-great uncle, but the English language has not had a need to get that specific and complex about such distant relationships.