English sometimes uses a double possessive, a structure like a friend of mine or that idea of John’s. It combines of with a possessive form.
This pattern is common and natural. It often suggests one person or thing from a larger set. For example, a friend of mine means one of my friends. That idea of John’s means one idea that belongs to John or came from John.
This is why a friend of me sounds wrong. After of in this pattern, English uses a possessive form, not a regular object pronoun.
- Correct: She is a colleague of his.
- Correct: We visited a neighbor of theirs.
- Less natural for this meaning: She is my friend.
The meaning can be slightly different from a simple possessive. My friend identifies the person directly. A friend of mine often sounds a little less direct and highlights that the person is one among several friends.
You will hear this structure often in everyday English, especially when introducing people or referring to one example from a group.