Many years ago, my ex and I went on holiday to a place called Ancora in Portugal where we met a newly married couple. We ended up doing some of the same trips and then the holiday ended and that was that. A couple of months later, my ex, my late father and I hired a boat and pottered along the Thames on it for a few days and one day decided to stop at a small town for supplies. Whilst in a local shop, we bumped into the wife of the couple we'd met in Portugal. Apparently her parents lived there.
The following summer, myself and my ex went to an air show in Wiltshire where I have family, and realised the man that was waving madly at us from across the field was her husband who was in the army and was giving a demonstration. Sadly, that was years ago and we've never seen them since.
Another time when I was on Orchard road in Singapore, I heard someone call my name and it turned out to be someone that I'd met while living in Germany! It's a small world...