"I assumed someone here would know my parents," returned Draco smoothly. He's spent most of the wedding playing the role of the perfect pureblood heir--as someone who clearly knew the roles and traditions that such a person played in wizarding society and who knew how to act at such a formal and important event in the pureblood world. And he'd managed it, quite well. He was the perfect gentleman, and the perfect date, or so Draco though. Yet somehow, he thought that Ginny may be disappointed. He wasn't the bold Gryffindor who would willingly run off to the corner to snog his date during a slow point in the wedding, for instance, and he certainly wasn't the kind to skip out on any part of the event--as Draco knew it would go noticed when and where someone like himself would disappear. He was just too much of a well-known wizard to hide from that aspect of life, unfortunately.
And when Ginny had said her family name, she needn't have gone into detail. Draco had memorized the pureblood lineage, after all, and knew that the Prewitts were the ones distantly related to the Blacks, and that they were the kind of family to cling to that sort of prestige. He also knew that as he was, technically, the rightful heir of both the Black and the Malfoy lines, that he was one of the most important guests at this wedding. To attempt to make amends for this, to Ginny at least, Draco kept an arm around her waist. Now that he'd really seen what the Prewitts were like, and he'd made somewhat amends with the other Weasleys in attendance, Draco felt more comfortable where he was.