People who have taken an ancestry DNA test and accidentally uncovered a family secret, what was it?

My story is not with a dna test but with a blood test. when I was 18 (now I'm 19) I started to donate blood, and, in my country, the first time you donate, they give you an "ID", with your name and you blood type.

The thing is, in my 18 years I never knew my blood type because my parents "didn't know it" (I believed them because they come from a rural environment so it was credible), then, some time later, they told me their blood type (I don't know if it was their real type or not, i really don't care), and my sister and I started to speculate about what could be ours and so on (without suspecting anything, of course).

Then my blood ID arrived, and some months and donations later, our parents told us that we were adopted, and that's why they hadn't told us our blood type.

/r/AskReddit Thread