A friend of mine and I are having a discussion about the back story of one of my D&D characters. He was born of a Noblewoman's dalliance and being bastard-born has caused him to be a bit of an outsider. My friend is saying that since his mother was noble he wouldn't be considered a bastard an would have normal social status. I tried finding relevant info on the web but couldn't find anything indicating that the gender of the noble parent mattered. He is citing Crusader Kings as his source.
Tell your friend he is completely wrong. To be illegitimate is to be born out of wedlock by definition (in a European medieval context). This applies to both genders and across all social classes (if anything it was more important among the aristocracy).
Marriage was not always formal, especially among the 'lower' classes, and not always important in all regions across the c.1000 years that constitute the Middle Ages. See this post with appurtenances for more information.