the adventurer in question was tortured which could have led to the information being imparted.
Well, if he was tortured, you got a torture report out of it. Was there anything in the torture report to indicate a relationship? If not, then this assertion is without merit.
However, I have intended to role-play that character as wholly unrelated to anyone else, once he got good enough at being an advy to warrant approaching nobles for trades.
Adventurers
are related. How anyone could possibly know about it is a completely separate question.
The very idea, on Dwilight, that a noble could be related to a commoner is ridiculous.
... because bastard-born children simply don't exist, right? I mean, that would
never happen.