When you were just a very young imp, Lin and Joe (your parents) sent “Mildred” (AKA: “Millie”) a letter with a photo of you in it, to show her, her new younger sibling

One day years later, you ran away from home (probably to escape a punishment) and you went to the city, “imp City”, looking for a place to hide, you eventually hide behind “I.M.P” and Millie and Moxxie come out after a couple hours

Millie: “Work was fun today dear.”

Moxxie: “It sure was Millie.”