Odd Cemetery Coincidence

In the town where I work, I walk around a local cemetery's paved roadway at lunchtime, for exercise. It's like a large park, pretty much safe from traffic except for occasional gravesite visitor's traffic, and I like to pass the time by reading names and dates on headstones, and wondering what their stories were, especially the ones who died young. I randomly stopped at one headstone, spying it from about three rows back from the path, as I was passing by. It belonged to a young-ish couple, who had died a few short years apart from each other, both in their 50's. I had not known either one of these two people personally. Never heard of them. I just glanced at their headstone, and noticed the dates were close together. I wondered what each one had passed from, at such an early age, and what their story might have been... ? When I got home, I looked up their obituaries online. The husband first .. had died in hospice from some unnamed illness. The wife, died a couple of years later or so, also after some sort of illness. Then I read her survivors' names...... Turns out, _her sister_, had been my very next-door neighbor, (we had shared a backyard, with a split rail fence down the middle), for many years, before I moved away to a new house in another town. I was a bit stunned by the coincidence, and being drawn to that headstone. I had never met anyone from my neighbor's family, we weren't all that chatty, (but not unfriendly), so we never talked about family names or stuff. so.....just a weird coincidence. :)