Declaimer: I do own neither Harry Potter nor Twilight. Those obviously belong to J. K. Rowling and Stephanie Meyer…oh but this interesting little story belongs to yours truly ;). Since the same actor played both roles in the movies, I've seen a few stories try to come up with a more "creative" explanation for this to suits "both supernatural universes"—usually having Edward and Cedric being one and the same person, or just distantly related—or just a "fluke"—someone has yet to use my idea, so here goes…
Tell me what you think! Be kind! This is my first fanfic!
The prologue here takes place between the 5th and 6th Harry Potter book and shortly before the Twilight series—and, yes!—I'm aware of the "official" time periods of the Harry Potter series being during the 1990's, but we can't be picky if we want this story to work—so please, bare with me on this one. There may be a few things I will be "tweaking" throughout the story, but I'll try to remain as faithful to the books and/or movies as much as possible.
"Explain that, Amos!" Dumbledore said in a harsh tone as Amos Diggory lifted his head up from the silver pensieve.
"I-I-I-I cannot, "Amos stammered, utterly frightened.
"You cannot explain why I saw a young man matching your deceased son's exact face and build in the form of a Mortifer vampire, in a barely-known township somewhere in America? A vampire, who, I was told, can pick up on thoughts of those around him, not to mention, is supposedly over a century old?" Dumbledore looked at him, his blue eyes burning.
Suddenly, an immeasurable amount of realization followed by regret washed over Amos' face.
"Oh…my God…" he whispered, "there is only one possible explanation."
Dumbledore continued to stare at him. "Is Cedric not dead?"
"No. No...he's gone…I'm sure of it."
"Forgive me, Albus," Amos whispered, his voice cracking, and his eyes rimmed with tears of despair, "I have committed a terrible act; I have violated the laws of Time itself…as if Cedric's death wasn't punishment enough."
Albus stared at Diggory for a long time, before speaking, unsure as to where this would lead. "Amos…you know who that was I saw."
"That…," Amos' voice cracked, trying to control his anguish, "that was not Cedric…"
Amos sniffed loudly, shaking his head slowly, then took a deep breath, "...that was his twin brother…Edward. Cedric…you see, Cedric was never my biological child…"
"What?" Dumbledore rasped, realizing also that his slight memory manipulation had worked—Amos knew that strange golden-eyed vampire's name as well.
"His real name was Cedric Avery Masen…and he was born in America—Chicago, to be precise…". There was a pregnant pause before Amos continued.
"…In the year 1901." Dumbledore's eyes widened with horror.
"Oh God…I knew this would come back to haunt me one day." Amos then began to weep desolately.
Dumbledore could just barely absorb the information that he had just learned, before he spoke again.
"Amos…what have you done?"