"Oh." Remus didn't know what the boy thought he could've been interrupting. His thoughts, perhaps, Remus figured. He did have a way of looking pensive. "No need to worry about that sort of thing."
A moment later, he turned back to Remus with a puzzled expression. "How do you know? Did someone tell you how you were going to die?" The history books hadn't been particularly detailed when it came to Regulus' death, barely glossing over the event. There was a younger Black sibling and then there wasn't. No book Remus had read had gone into detail on the subject and over the years without jobs or prospects, Remus had spent much of his time in public libraries, reading up on the first war.
So either someone had read even more books on the subject than he had, which was somewhat doubtful, or whoever had told the boy had been present when it happened.