Princess Serenity was the Princess of the Moon Kingdom during the Silver Millennium. She would often sneak out of the Kingdom to Earth where she met and fell madly in love with Prince Endymion. When the Moon Kingdom was destroyed by Queen Beryl and her evil forces, Queen Serenity sacrificed herself to reincarnate Serenity, the sailor guardians, and Prince Endymion on Earth to live happy lives. Unbeknownst to Usagi Tsukino, she is the reincarnate of Princess Serenity.