I'm really lacking in background of the setting, but a couple things occurred to me from what you wrote:
- Prevent the PCs from following the prince by having those who have a vested interest in seeing the old will carried out attacking (by whatever method: daggers, spells, court) the holder of the new will.
- Have Yorge invoke a heroquest known to kill the primary questor, but which requires the heroes in secondary roles. (Like that western Hrestoli quest.)
Mike Dawson