Severus remembered, vaguely, that Potter had expressed his wish to apologize in person. But he hadn't been quite prepared for him to spring the apology on him, just like that. When he did, Severus felt his mouth open and close a few times before he managed to even clear his throat. Though that was really all he'd wanted to hear from the boy for years, coming from the man Potter had become, it was ... humbling, to be sure.
"Thank you, Potter," he said quietly, and then he cleared his throat again, because it seemed to have developed something of a lump. "That -- means a great deal to me." He supposed he ought to apologize in turn for how he'd treated Potter when they boy had been in school, but somehow he couldn't quite bring himself to, because, well, he wasn't entirely sorry for it. He had only been trying to protect him, after all, when his incessant rule-breaking put him in harm's way.
On the other hand, Potter more than likely realized that, considering he'd said he had been more tolerant of him than he would have been, if the situation had been reversed. Before he managed to say anything else at all, however, Potter had changed the subject, back to his father and godfather. "Well, if it is any consolation at all, they likely won't treat you with anything approaching the same contempt as they treated me. You aren't ugly, greasy, and in the wrong House, after all."