Regulus of Hogwarts: Lord of the Stars

Somewhere in the distance, the Fiendfyre gave a muffled roar, like a great dragon toppling something over. Stone and flame tumbled down together.

Voldemort withdrew from the mental space and said nothing for a while. His gaze stayed on Regulus's face, the vertical pupils contracting slowly, as though pulling something into focus.

Then he spoke. "Dumbledore."

It wasn't quite a question, nor a statement, and barely sounded as if it were addressed to Regulus at all.

He'd only spoken the name, the way one might read a familiar title aloud while leafing through an old book.

There was something faint underneath it, too thin to call mockery, too thin to call anything, nearly transparent. But it was there.

He had seen the parallel memory: Dumbledore's magic and his own, laid out on the same plane.

Regulus's expression didn't shift.

So Voldemort had found the memory. The arrangement had worked.