One has to feel sorry for Primus. As the story progresses, he's shown to be a pretty nice guy, eventually letting Tristran travel with him as he heads up to find the topaz. He finds the star at an inn, and the topaz, and she prepares to give it to him, then Tristran uncovers the whole scheme to kill the star and the Lilim queen kills Primus in a rage
The final moments, starting with Tristran's death and the fact that Yvaine can never return home and the final lines: "They say that each night, when the duties of state permit, she climbs, on foot, and limps, alone, to the highest peak of the palace, where she stands for hour after hour, seeming not to notice the cold peak winds. She says nothing at all, but simply stares upward into the dark sky and watches, with sad eyes, the slow dance of the infinite stars."
The deaths of some of the prince's were worse than others. Primus murder just after talking to Yvaine might count. Poor man died in a bathtub, not exactly the most dignified way to go.
The poor Bishop who accidentally gets poisoned along with Tertius, and just after telling Primus he'd make a good king.
Septimus even had an element of tragedy to it. If your willing to forgive his killing of Ferdy, his bullying of Bernard and his beating of Captain Shakespeare.