When I got my DNA results from ancestry I was a bit surprised I had no matches for my maternal grandfather, but I thought some would turn up. Meanwhile I had a very strong match group of complete strangers from an area of the country I had never been to and had no links with. I put them together into an extended family and followed the branches down to the 1911 census, guess what, one of them was living right across the road from my mother's family the year after she was born, and living in the exact same house which our family bought from them the following year, the family home to a whole generation. I have lots of medium matches to my maternal grandmother's family from descendants of cousins who my mother actually knew, but I have even stronger matches to the family across the road. They are my strongest match group on Ancestry, 6 out of my top 10 matches. The mother was one of four sisters and I have descendant matches to all of them, plus some descendants of cousins of the couple. Two matches are my strongest ones on Ancestry, 109 and 106 cm. I still don't have any matches for my grandfather, and not for lack of trying. I have been researching his very interesting family for over 50 years and have a huge tree, it was my main interest in geneaology, so I was a bit put out to say the least!
There was only one man under the age of 80 in the house across the road, and he was an office worker the same age as my grandma's sister, who was a typist and was known in the family as "the flighty one"! For various other reasons I think she was the mother of the baby and my grandma and grandpa adopted her secretly to hush up the scandal. I will never have any documentary evidence, the birth certificate shows my grandpa as the father. I have changed my grandpa to non-biological, but do I have enough information to show myself on my tree as granddaughter to the man across the road? Everyone who knew these people is dead now except for myself and my brother. My mother who died 9 years ago was an only child, her aunt (probable mother) died in 1942, and the man across the road died in 1946. He had another daughter but she died childless a few years ago. Also, if I leave my grandma as the mother, I don't want it to look like grandma did the dirty on grandpa! But I don't have any actual evidence, other than circumstantial, that my great aunt is the real mother either. The DNA connection for both of them to that family would be the same anyway, I presume.
All advice gratefully received.