Is this sentence correct?
A father of mine is ill.
The following sentences are correct:
My father is ill.
A brother of mine is ill.
The second sentence implies that I have at least two brothers. The sentence “A father of mine is ill” would usually not be correct, because people normally have a single father. “A X of someone’s” cannot be used if there is only one such X.
If you say “a father of mine”, it implies you have two fathers, and that they have no overwhelming distinguishing feature. For example, if your parents are divorced and your mother remarried, then you might say “my biological father is ill” or “my stepfather is ill”. The same goes for “a parent of mine”: you would normally say “my father” or “my mother”.
If you were raised by two men, which is highly unusual in English-speaking societies, then “a father of mine” would be correct. But because it is an unusual situation, that sentence would definitely surprise your audience unless they knew about your family situation beforehand.
Source : Link , Question Author : Anixx , Answer Author : Gilles ‘SO- stop being evil’