Queen Diana was the ruler of the Moon (or as it was called then, Luna) in the age before the Silver Millennium. After hearing a prophecy from the powerful oracle Neherenia that she would come to rule the entire solar system, she allied the planets with her using intimidation. The Moons, unwilling to accept her ruler ship, resisted Queen Diana and were destroyed for it.

Although Queen Diana was Queen Serenity's mother, she was long dead by the time Princess Serenity was born. Strangely, there are no records of her death.