In one playthrough I was close enough with Lisle that he told me his secret. During the negotiations in week 7 I was given the option of revelaing that secret or not.
in another playthrough Lisle didn't tell me himself, but I found out anyway through exploring the castle. In this playthrough the option to reveal the information never came. The whole thing wa just never mentioned again. Seems odd since a player who found out by sneaking seems more likely to want to reveal it than someone who's friends with Lisle.