A friend of John's?

[Baby boomer]

Please can you tell me whether it is correct to say, "He is a friend of John's", which is the almost universal usage but looks incorrect, as opposed to, "He is a friend of John". I suspect the "double possessive", so to speak, may be acceptable since it is correct to say, "He is a friend of MINE," rather than "He is a friend of ME". However, I should be interested to hear whether I am right. Thanks!

[svartnik]

Please can you tell me whether it is correct to say, "He is a friend of John's", which is the almost universal usage but looks incorrect, as opposed to, "He is a friend of John". I suspect the "double possessive", so to speak, may be acceptable since it is correct to say, "He is a friend of MINE," rather than "He is a friend of ME". However, I should be interested to hear whether I am right. Thanks!

A friend of John or a friend of John's ?