Sixteen years ago, when Grindelwald first met him, he had been nothing more than a wailing baby. Nurmengard was clearly no place for a baby to survive, so Grindelwald contacted his old followers and sent him to an orphanage.
Six years ago, when Grindelwald met "him" for the second time, he was already an Obscurial. By then, he had become an idiot who could do nothing but eat, drink, relieve himself, and sleep.
Having had an inextricable connection with Obscurials, especially those of the Dumbledore family-Grindelwald insisted that he belonged to the Dumbledore family-he tried to train Edward, hoping to turn him into a special Obscurial like Credence.
Then he failed.
After nearly half a year of instruction, the idiot was still an idiot. Grindelwald lost interest in him and sent him back to the orphanage.
Three years later, at the point when Edward transmigrated into this world, he "returned" to normal and received his acceptance letter from Hogwarts.
When Grindelwald learned of this, he contacted Dumbledore and told him the truth about Edward's situation. Sure enough, Dumbledore also took a keen interest in him, even going to the orphanage in person to bring him to Hogwarts.
And that was why Edward received such special attention from Dumbledore.
"But why are you so certain I must have Dumbledore blood?"
Grindelwald's tone was calm. "Do you think I would tell you something I've kept secret even from Albus? Still, I can tell you that I'm not being cryptic for the fun of it. I simply promised someone I would keep this secret."
"That person... has something to do with my background?"
He nodded in confirmation.
Dumbledore left before long. Perhaps because Edward was there, the pair of "friends" did not talk much. Grindelwald quickly got down to business, seemingly intent on