"All right," Regulus agreed instantly with a slight nod.
It was fair enough, really and he could understand it, though he had meant no harm in the comment about Harry. He could also hear the honesty and the strained undertone to James' voice. In that moment, he truly felt a bit bad for James, another sentiment he hadn't ever expected to happen. But he hadn't really ever had anyone, not in the same way that James had, and he couldn't imagine that it was easy to come back and find that his son had become fully grown. And while he was completely certain, he didn't think Lily had returned either. And everyone knew how in love James was with Lily.
So he just agreed without any hesitation and left it at that.