Spoiler
The princess Dirk, Charlie's adopted brother, married in the beginning of Tress is a member of a Selish Secret Society with a plan to kill the Sorceress.
What evidence is there for this you ask?
- The name of her kingdom is Dormancy, proving is connected to Sel
- She is described as exceptionally beautiful and her hair shimmers, which clearly indicates Investiture based beautification
- She appeared on Diggen's point shortly before Tress started the journey that drove the Sorceress off-World. Which means her Selish Secret Society has an ability similar to Hoids ability that pulls him to where he "needs" to be.
- She married a War Hero, who is clearly the strongest Sorceress Slayer on Lumar