Regulus could feel his frustration growing. No, he didn't bloody know what had happened to him. He didn't know why he had died at the age of eighteen in the service of the Dark Lord and he didn't know who had killed him. He didn't even know precisely what betrayal had led to him being killed. Worse of all, he could detect the change in Sirius' temper. It was wearing down on him, this constant reminder that they weren't supposed to be on the same side, and the only thing that was thinly connecting them was a tentative brotherhood that was based on a childhood where they had been friends. It was going to take a lot of work to get past the fact that they had been enemies for so long, and each moment of Sirius being reminded that he had been a Death Eater seemed to hurt any chance they had of moving forward.
He listened silently at his brother's dismissive comments about the recollections of his death, because they sounded true enough and Regulus didn't know enough to second guess them. He did flinch a bit at the sound of his former master's name. It was a reaction that he was hardly able to help, though he tried to conceal it the best he could.
"Please, if you know anything, just tell me," Regulus said in a bit of a sigh, preparing himself for the worst, and wondering if this was something he really wanted to learn while Sirius was in close proximity. Still, it had to be a good sign that Ron seemed willing to discuss the subject in front of both of them, right?