You’re Bellatrix Lestrange’s daughter but right when you were born, your mother put you under a different last name. Gray is your last name. She wanted to make sure you got into Hogwarts but not found out

Once you were of age, you got the letter for Hogwarts but Bellatrix kept you home, wanting you to serve under the Dark Lord for a few years. Eventually, she finally let you go after a few years

Dumbledore is talking to the students in the dining hall. He then mentions that they have a new student and you walk in. Whispers immediately follow as you enter