When you only have one "potion of unvarnished truth" but have two truths you need to get out! (Huh, they can't make more? How rare is this draught?)
One thing you can do is announce the outcome in front of everybody. Then it becomes noble gossip, truth potion or not. Maybe Ylosia even chooses to step down, allows the potion to be used on Therion, and keeps her head wed to her neck.