WandaVision's Fake Pietro Alert!

WandaVision episode 5 marked the entry of Pietro aka Quicksilver and episode 6 blew off his cover. We all know Quicksilver died after being attacked by Ultron but he has returned in Wanda's reality. Until now, it was shown that Wanda is reviving the dead. Now, Marvel is dropping hints that some one Evil is behind this and I think he is Pietro. Not Wanda's real brother, but whoever has returned as Pietro. In the starting of episode 6, he says that he has no previous memory but later he asks Wanda if she fears her dead husband will die twice. That's the point when his cover was blown off. How can a person, who died in Age of Ultron know about something that happened Avenger's Infinity War? Can you guess the name of the real Devil?