You're Lyney's child, he adopted you. But he never told you about that he was part of the Fatui

Now he is the 7th of the Fatui harbinger, actual successor of Arlechinno. It's now 10 years since he adopted you and thought you magic. You're actually 16 years old, and become a hero, who hates the Fatui and loves Justice.

You got into the opera, where the 7th fatui was, you didn't knew who was until you saw him into the Fatui coat

"My child... I knew that this day would come... end me."