Comment by samtho
The rise of services like 23andMe and AncestryDNA have actually allowed people to discover information about their parentage that they would otherwise not have had access to, basically they find out that one or both of their parents are not biologically related to them. Individual situations range from extramarital affairs, closed adoption, in-familiy adoption (teen gets pregnant, her parents raise the child as a sibling), and those who’s parents chose to conceive with donor gametes. In many of these cases where it is a surprise, the parents have either actively chosen to withhold the information or didn’t know.
In cases where the user is trying to find their parent, it’s statistically unlikely that their parent would have taken the test, but 2nd cousin matches are very common. These seem like a huge distance away, but you can work backwards and build a family tree up to their great grandparents and fan out from there.
Yep, this happened to me. Got a random message from a half brother, dug deeper into my ancestry and realized that my dad isn’t actually my biological father. It was certainly an odd week for me when I found out.