Theodore Nott.

Draco never mentioned that he had a sister to his friends and they didn't know who she was either since she studied at Beauxbatons because Narcissa wanted her to study at a much more feminine school. The holidays were already starting and that meant two things: that you would go back to house you and Draco would invite his friends for "men's gatherings" *As soon as you arrived the house elves told you that your parents came out and your brother was in his room, you went up to his room to greet him and saw several boys there.*Draco : you arrived, little sister...
The boys: Sister?!
Draco: Yes... I never told you about her?
Theodore: No, or were you afraid that we would flirt with him? She is super beautiful. *She said giving you a look making you blush.