Friend coincidence

About 13 years ago my daughter started a new school and made friends with a girl in her class. I got on really well with her mother who was older than me and we became good friends meeting up and socialising. A while before this I had gone back to university part time in a different part of London and had got in with a group of women who I also made friends with and socialised with. Amongst this group was a woman a few years younger than me. These separate friendships continued for some time and at an event my university friend turned up with her partner and children. For the first time we talked about children and where we lived and to our surprise we found we lived close to each other and our children went to the same school although in different year groups. We made an agreement to keep an eye out for each other the next time we were picking our children up. A while later I saw my younger friend at the school and she was talking to my older friend. To my amazement when I went up to talk to them I discovered my older friend was actually the mother of my younger friend and my daughters best friend was her very much younger sister. We had no idea of the connection until that day at the school. All these years later we are still all good friends and our children are now grown up..