Jeyne Heartley, known as Nathaleya while employed by the Zul Joriin was the only trueborn child of Meryanne Heartley and the half-sister of Emeric Blackgard - with whom she developed a romantic relationship with. Nathaleya was the handmaiden of King Althurin I and the personal caretaker of Prince Emeric Blackgard. She was in fact a spy of Sofina Blackgard tasked with gathering as much information as possible.
Her death in the Battle of King's Landing and the revelation that she and Emeric unknowingly committed incest with each other deeply embittered and hardened Emeric - with some believing it was a contributing factor in his ambitious - though arguably delusional - desires to conquer the World.