I ran into a college roommate from 20 years prior, both of us in a m4m chatroom yet neither knowing the other was gay for the year we'd lived together. I thought I recognized something familiar about the screenname so I sent a message asking specific questions. He freaked at first but we had some good conversations. Called, kept in touch for a while but then lost track of each other again. He's a nice guy, very smart, we get along well, just no real chemistry between us.
Also in a m4m chat room I've run into a grandson of a very famous guy (I won't say the name), his ancestor being a close colleague (probably also a friend but I don't know that) of my grandfather's brother, both from the entertainment biz back in the early 1900s. He of course knew of their association but also didn't know how close they might have been. We only chatted that one time but it was a long and nice conversation. Him being married I was somewhat surprised that he ID'd himself but not surprised that nothing more developed from that.
But that generations after our relations had relations, we'd run into each other online? It's a small small internet.