He Thinks She May Not Be His

Ok guys let me know what you think. A good guy friend of mine has a daughter who is still under age but nearly grown. She was born when he was quite young and her mother who was a teen. They were both very promiscous teens at that time. Well he expressed to me that he always had fears the child may not be his and is eating him up inside. He is no longer with the mother and has not been for a long time and is a single dad. I know both parents and she looks nothing like either one. I know that may not mean anything but come one, usually kids get something noticable from their mom or dad. It's nothing from either of them in this case. The child has eye color neither of them have, very distinct shaped eyes and a very prominent nose. I can find nobody in thier families she resembles. She is also verrry tall, I am talking about 5'11 and neither of her parents are over 5'8. She is taller than almost all the men in her family on either side. He says that she is his daughter no matter what and will love her as such, but he wants to know. What is a good way of finding out without expressing these doubts to the child?He would like to know for piece of mind and medical reasons should there ever be any. He doesn't want to tell her because she has no idea there is an issue.

I thought it would be best to get a man's point of view, or anyone else's.

Thanks,
lootie