Queen Nehellenia and Queen Serenity both share the same origin. They both came from another galaxy. She was sealed inside a mirror by Queen Serenity. Queen Nehellenia is the main reason why the Silver Millennium fell by placing a curse on baby princess Serenity. Queen Nehellenia used her powers to capture Elysion, a sacred sanctuary inside a dimension in the center of the Earth that protected the Earth. Her powers literary wilted the holy sanctuary and caused the death of many of its people. Her curses turned Helios into a Pegasus and her presence on earth gave Serena and Darien a curse. The curse appeared as shadow on their lungs and when the curse was activated the two were turning into children and were continuing to un-age from an immunity deficiency.
She is later stated as an incarnation of the being Chaos.