So some background: 3 sessions into the campaign, we arrived in Neverwinter and went to the nearest inn. At this inn, one of the barmaids started to flirt with our Paladin. Our paladin had sworn an oath of celibacy, and when the serving girl found her flirting didn't work, she started to work again. However, for laughs, our Rogue tried to make a CHA check to seduce her. He rolled a 20 and they ended up in the barmaid's bedroom. At this point, we decided to call it for the night.
The problem is that in my GM notes, this barmaid was actually the Rogue's sister, who was kidnapped at a young age. In addition, the entire storyline I was planning on going with is that the people who kidnapped his sister are also the people who the party is currently tracking down for other reasons. There are also other plot reasons that make it so I can't easily just make her a childhood friend retroactively. For example, the barmaid possesses objects and knowledge that only the sister would be aware of.
You probably understand my issue:
- Keeping the barmaid as his sister could cause conflict both at the table (Rogue to GM: "why did you not warn me she was my sister, GM?") and on the table (Paladin to Rogue: "Why would you commit such an unlawful act?");
- Rewriting part of my campaign to remove the surprise incest would be a lot of work;
- I did see a 3rd option of starting the next session with a short segment in the sister's bedroom the night before, where either the sister or the rogue notices something peculiar about the other person. However, this would be the first time that we do not skip the night between 2 sessions, so that would put up warning lights. The other players might think the wrong idea when I take the rogue apart for some personal GMing.
I'm not sure how to handle this. Part of me wants to see the looks on their faces when the reveal happens, but the sensible part of me thinks that might cause irreparable damage in the group. However, the alternatives would invalidate much of the work I already did on this campaign.
How do I deal with this situation?