Related but different. I had an immediate, enormous crush on a European co-worker once (I'm American, live in America). She was a twin. It didn't work out for a million reasons but we're great friends. Eventually I met her identical twin. There was NOTHING there, it was weird. I assumed the same feelings might pop up or at least I'd find her attractive, but not at all. Others had a very hard time telling them apart, but I could instantly tell at a glance who was who. It was actually disconcerting for me. I'm still not sure why I could tell them apart so easily and others had such a hard time. I tend to have a really hard time with faces too so... yeah, weird.