Who convinces Julian to plot a rebellion on Sigismund's behalf in the play, The Tower?

Julian is the governor of the tower in which Sigismund has been locked until the age of twentyone. Julian is influenced by the physician to convince the king that Sigismund be restored to his rightful place as heir to the throne. When the king sentences Sigismund to death for attempting to rise up against him, Julian plots a rebellion on Sigismund's behalf.