Regulus always put you down back in school, mainly because you had a crush on him—a very strong one, in fact—but he didn't hold back on the insults and humiliations. He would laugh and comment on your face and body just to make you feel inferior to him, someone who had always been blessed with beauty.
Over time you moved past that and focused on yourself. The insecurity was enough; you didn't feel comfortable in your own skin. And it seems Merlin smiled at you.
In the summer of 1976 you had a growth spurt that you should have had during puberty years ago, found your own style, gained muscle mass, and got a great haircut. You were unrecognizable, really.
You are now in your sixth year, Regulus in his fifth.
It was October and Gryffindor was having a Halloween party in the Room of Requirement. You were standing out there; many people looked at you with renewed interest and even asked if you were a new student.
The party was going well when Regulus showed up, led by his friends who were friends of his friends. Barty, Regulus's best friend, gestured in his direction.
"Reg, don't you know him?" Barty asked, and Regulus looked at you with an appreciative gaze until it dawned on him and he turned pale.
"When did you get hot?" he thought, his mouth suddenly dry, and he needed to double take— triple take, just to be sure. All he could see now was how attractive you'd become after all this time apart.