Where Harry Potter meets Percy Jackson

• In Greek mythology, "X" was the only child of King Menelaus of Sparta and his wife, Helen of Troy. 
• "X" was nine when Helen left with Paris.
• While Menelaus was fighting the war at Troy,"X" lived with Aunt Clytemnestra in Mycenae.
• "X" married Neoptolemus, also known as Pyrrhus, son of Achilles , ten years after the end of the Trojan War.

Id "X"

Answer (highlight to read) : Hermione