Josephus may have adopted the story as he was Jewish , but Manetho was a Egyptain Historian, it seems this all occur arround the time of Akhenaten , Ramesses1 and his son Seti, since Ramesses1 tried to wiped out all of Akhentaen`s history.
Amenhotep IV / Akhenaten 1350 - 1334
Smenkhkare (Ankhkheperure) 1336-1334
Tutankhamun (Nebkheperure) 1334 - 1325
Ay (Kheperkheperure) 1325 - 1321
Horemheb (Djeserkheperure) 1323 - 1295
Ramesses I (Menpehtyre) 1295 - 1294
Seti I (Menmaatre) 1394 - 1279
Actually he wasn't. He was an Egyptian Priest. There were no historians in the modern sense back then. More often than not history, myth and legend became intertwined. As can be seen by previous mentions of Amenhotep and Ramesses, also called Seti. All the priests back then really had were names, with no real historical knowledge of who they were or even their backgrounds. This is not a good basis for making the claims that many have tried to make.