As such, any uncle of hers would be minor royalty, even if illegitimate. (daum.net)
When I saw this structure, I would thought that the preposition ‘of’ presents a set (=a set of her uncles) and ‘any uncle’ is part of the set. But reading this sentence - “Not me, exactly, no. It’s this friend of mine who has a matter to talk over with her” - from a novel, Dona Flor and Her Two Husbands, I would think ‘of’ means ‘that belongs to; that has the property of’. I’m afraid some would say it’s not a big deal. But isn’t it worth to think of, or to be told about from sincere natives?