If you go back ten generations you have 1024 ancestors in that generation (but some could be duplicates if some of your ancestors married cousins). Eleven generations back you have 2048 ancestors, etc. So it seems virtually certain that everyone has some ancestors who were born out of wedlock...if not in the most recent 11 generations certainly in an earlier one.
Many people are proud of noble or royal ancestry--which pretty much guarantees having illegitimate ancestors (such as William the Bastard, later known as William the Conqueror, or Charles Martel).
I personally don't know of any illegitimate ancestors but I'm sure it is just because I haven't been able to go back far enough tracing my ancestors. I did find one great-great-great-grandmother who was born 5 months after her parents got married. Born very premature, no doubt.
Interesting. I do have a nephew, who was born prior to his parents’ marriage, and I have another nephew who already had a child with his pregnant bride, when they got married.
The actual biological parents married one another in both of those situations, so neither situation seemed to be “scandalous”.