Regulus stops walking for a moment, looking at Harry fixedly and rather strangely. At last, quietly, he says "I'm not sure I even knew Andromeda had a child. Let alone a grandchild. I..." He frowns, passing a hand over his face, and looks away. "Draco and I didn't talk about it much. Not after I first arrived."

And now, he can't help but feel guilty for that. Perhaps it's a mark of how he's changed since arriving here, but he feels a deep and uncomfortable shame at the realisation that he never even wondered about Andromeda, in all of the introspection and all the consideration he's given to his life back home. When she was blasted off the tapestry, in a very real sense, she ceased to exist to him. That...

He still struggles with some of what he's been told is wrong. But that, now that he looks at it face-on, is definitely wrong.