I am interested in genealogy and was researching my son's partner's tree when I came across a person in that tree that was also connected to my family tree ! A first, I thought that I was on my family tree.
I emailed her and it turns out that she is my 4th cousin on my tree, but ALSO my son's partner's 4th cousin on her fathers side of the family !!!! What a co-incidence that is !!!!
Also, when I found a new sister I didn't know I had 11 years ago, her son's birthdate was same date (different year) to my son.