Prudence Halliwell never died because she was in fact the Goddess Hecate, her supposed death was actually her shedding her mortal form. She hated lying to her beloved sisters Piper, Phoebe and Paige but that was the Olympian policy she was not supposed to reveal that she was actually a goddess. Percy has been betrayed so he left Camp Olympus, he went to Hecate to remove his scent and she offered him a chance to partially leave the world of the gods, once he did, he met the other Halliwell sisters. This may be a one shot
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