How do I find out if my firstborn is legitimate?

My wife turned out to be an adulteress and I'm not the father of our fourth child - one of my vassal dukes is. I guess I was too busy ruling an empire and not paying attention to my wife enough (I'm sure homosexuality had nothing to do with it).
My firstborns are treated as descendants of my dynasty and there were no events related to me being suspicious of their ancestry. For the purposes of game progress and scoring - they are fine members of my house. Still, for the sake of storytelling I'd like to find out if they are really mine.

Is there a way in the game to find out who the real father was? Intrigue event chain? Paranoid-trait related, etc.? If that can be done using cheats - that would do, but I'd like a valid game-play way too.

Update: so with charinfo 1 I can bring up who the real father is for a character and see authors of the pregnancy-in-progress. Any in-game events for finding out parents of kids born for some time now?

Solution 1:

The intrigue focus's 'spy on' tombola event (WoL.2060) can fire the "opportunity to accuse of crime" event. One of the possible accusations is:

Illegitimate (no known father, or known father is not real father -- you also find out who the real father is)

This requires the target to not be an independent ruler, and can only happen once per target. Luckily, 'Illegitimate' is the first available charge, meaning if this event fires, you either can expose the target's illegitimacy (learning who the real father is in the process), or you know the target is legitimate (plus getting the opportunity of accusing them of another crime).

Unfortunately, this event competes with 5 other events in the 'spy on' tombola. Some tips to maximize the accusation event:

1. Have higher intrigue than the target (breakpoints at 3, 5, and 10)
2. have a higher schemer level than the target
3. Ensure the target is not plotting (or backing) a plot, OR ensure that you know about that plot
4. Have temperate, just, kind, or honest.
5. Target does not have an embarrassing trait
6. Target does not have a modifier related to adultery