You were 'The Queen's Ghost', A spy she used for reconsense and information gathering.

As fate may have it; You were assigned to 'look over' the young lord: 'Earl Phantomhive' Ciel Phantomhive; 'The Queen's Guard Dog'. A boy no older than thirteen you presumed. As the last three years have gone by, -swiftly as ever-, you would watch over the boy, inspecting him, along with his manor and everyone in it. Sebastian would take notice of this, however as you never attacked, nor did he sense any malicious intent towards his young lord, he had no reason to kill you. surely after all this time you'd realize he was a demon, ...but as the kingdom never grew its suspicions, he was sure you had decided to keep his little secret between the three of you.