vassals finding out the ruler is illegitimate?

[ssnaumov]

I'm playing as a queen who has two sons with regular stats with her husband (matrilineally) and a genius son who is a product of an affair with one of her dukes. The husband doesn't suspect anything. I'm tempted to make a genius son a heir, but I'm also worried about the consequences of intrigue-focused vassals snooping on him when he is a ruler. Is it possible for them to find out his real father identity? And what might follow if they discover it?

[Yaldabaoth]

No that doesn't happen. DNA tests were not a thing back in the day.

[Michael]

The game basically decides whether the child's illegitimacy is going to be discovered or not at conception. If you made it through the pregnancy with no events popping up then you were not discovered and will never be discovered.

[ssnaumov]

Thanks! DNA tests were indeed not a thing, but when I spy on a vassal using Way of Life DLC's Intrigue focus I sometimes do find out they are illegitimate and I can revoke their title as a consequence. That made me suspect the same thing can happen when I'm illegitimate and they spy on me.

[Charlememe]

Vassals with the spying way of life can find out you're illegitimate which gives you an opinion penalty, around -20, which goes away eventually.

[A6M Zero]

I'm pretty sure that certain mods (AGOT mod I know for sure, maybe Ck2+) allow characters to investigate someone's legitimacy, but I've never encountered it in the base game.