So I went exploring today and found Castle Ledur and cleared it out like a good adventurer should. Even killed a prince and his bodyguards ... was a fun fight. However, I get Nina's key from him and open up the secret something-or-other door only to find out that it was the other end of the tunnel that went from the hatch in Ledur (the village). So, my question is to know if I did anything to ruin that quest line if indeed there is any more of that? Was I not supposed to kill the prince yet, or at all? I don't want to miss something that could potentially be quite important.
I should also mention that I'm not interested in spoilers. Just a simple, "don't worry about it," or, "you should go back to an old save game," will suffice.