Finding a friend and realising they are a relative

A few years ago my brother started work for a company in Northern Ireland (we are Northern Irish). My brother often talked about a friend who he had made in work called Frank. Frank was older than my brother, roughly between my parents and my brothers age. During the following summer My sister and I took my Grand Mother on a holiday driving round parts of Northern Ireland she had not been to since she was a child. This involved going to see old relatives and friends who my granny, who didn't drive her self, had not seen in many years. We visited one relative who was she was my granny's aunt, although this would make you think that she would have been very old it transpired that because of large families in Ireland, and because she had married into the family, marrying an older man, she was actually a few years younger than my grandmother. During the visit her son came home and started chatting to us about his work and other things, he was a relative who we had never met before so it was all pretty general. then he mentioned his friend at work Marcus - At which point we all realised that he was talking about my brother! Turned out that Marcus's friend Frank was actually my Gran's first cousin - Marcus's first cousin twice removed!