I would call him by his name. You do not share a common ancestor, so are not related.
uncle
uncle
Your father's brother is your uncle.
Aunty and Uncle.
philapple Uncle
Your brother's father isyour father, unless you are half-brothers. In that case, your brother's father might be your stepfather
Your uncle on your father's side is your father's brother.
Your father's younger (or elder) brother would be your uncle. It is tradition to call them by their given first name as opposed to 'Uncle', in the way the majority of people call their perents Mum & Dad rather than their given names.
uncle.
Your fathers brother is your uncle.
he is literallly like a second uncle to you
Great Uncle.