It wasn't Madara who massacred the clan. It was Obito (who was disguised as Madara) and Itachi who did so.Sasuke's one of the last remaining Uchiha, of course Maddy knows his name. He knew it back when him and Itachi massacred the clan.
Sasuke's one of the last remaining Uchiha, of course Maddy knows his name. He knew it back when him and Itachi massacred the clan.
Black Zetsu because that was how he was up to date with knowing the Uchiha are nearly extinct