I very recently discovered lots of great aunts and uncles on both sides of my family. My maternal grandmother died when I was 4 and I knew her three sisters and their mother (my great-grandmother) very closely while I was growing up. I always thought there were only those four sisters until my research turned up 4 more siblings, all of whom came to the United States. I also found their children (my mother's first cousins who I never knew existed) and am now trying to find their children - my second cousins, who I hope to be able to make contact with.
On my father's side, I never knew my grandmother had any siblings, either in the United States or in Lithuania (where my grandmother was born). In the last couple of years my research has found that my grandmother had 7 siblings, all came to the United States and I have met some of my new-found second cousins, who are helping with further research.