This was supposed to be an answer, not a comment, but I can not figure out how to convert it.
My poor half-aunt, Peggy Hughes ( https://www.wikitree.com/wiki/Hughes-20504 ) (1911-194) was both unwanted and forgotten. In all the family autobiographies (by her aunt, her brother, and her niece) there is no even an indirect mention. (And her aunt and her brother definitely knew of her existence).
I only found out about her in my mid teens, when my visiting grandmother (then in her 80s) was wandering around the house in the middle of the night saying "where's Peggy?" and "you can't leave a baby alone in its bed" over and over again. So of course I asked "who's Peggy?"
I didn't find out until the next morning.
Her parents' marriage had fallen apart shortly after she was conceived, and they separated. Meena (her other) definitely didn't want Herbert's child, and tried to get an abortion, but it failed. The baby was born very sickly, and Meena still didn't want to have anything to do with her (Meena was never a very good mother, even to her two sons whom she DID want). Eventually Herbert's parents, in Belfast, took her in, where she died at age 3 from pneumonia.
It seems that lots of people in the family had heard rumors about her, but nobody had any concrete information, until another cousin and I started digging into the digitized genealogy data. (That cousin was another family surprise - she did not know who her real father (my half uncle Pat Hughes) was until she had grown children of her own. And of course we knew nothing about her either.)