The Mermaid Queen's Revenge

Lucia is princess of the marine kingdom Dinelidia. She saw her uncle murder her parents to steal the throne. A blow to the head erased her memory. Her friend and the hotel manager betrayed her, pushing her into the sea. Nereo saved her, restored her memories and her magic tail. They marry to reclaim the marine kingdom. Lucia returns with her merman husband. Escaping her assassin uncle, Lucia transforms into the powerful queen of the ocean.