In chapter 5, if you romanced Triss the king inquires as to the nature of the relationship. I chose the 1st option which was we are close and its no one else's business. The king's reply was: no need to be rude, I too loved Adda's mother, they forbade me from marrying her but I hope you fare better, at least you are sterile so there is no chance of you having children. Adda's mother was Foltest's sister (the degenerate). This made me wonder whether Trissy is in fact Geralt's sister (and how would his royal highness know?). There are some convoluted legends told through in-game literature and tall tales that give some vague hints but nothing specific. Any ideas?