NOTE: A further aspect of my overarching thesis is that messianic Judaism began as a Ptolemaic response to the Seleucid Primary History. Specifically, the promise of messiah of the house of David found in Isaiah (and later transplanted to Samuel/Kings) was merely a recasting of the Nectanebos prophecy, which in the Alexander Romance, allegedly formed the basis of Alexander's rightful claim to sovereignty over Egypt.
Russ Gmirkin provides a good summary of the Nectanebos prophecy and its relation to the Alexander Romance:
Nectanebos II, the last ruler of Dynasty XXX, came to power in 359 BCE, the year before Artaxerxes III Ochus came to the Persian throne. In 351-350 BCE, Artaxerxes Ochus attempted to regain Egypt for Persia, but gave up the effort.1 In 343 BCE, Ochus led a second campaign against Nectanebos II, with 500,000 soldiers and 80 triremes.2 Marching his army south from Phoenicia, Ochus lost a significant number of troops in the bogs of Lake Sirbonis—an event that has been compared to the destruction of Pharaoh's troops trying to cross the Red Sea. Reaching Pelusium with the remainder of his army, he found the approaches of the Nile protected by an army of 100,000 troops of Libyan, Greek and native descent, manning fleets of warships, a string of border fortresses and other temporary fortifications. Thus defended, the Egyptians believed they could hold out until the rising of the Nile forced the Persian invading troops to abandon the Delta, but one of Ochus's Greek generals, using native guides, managed to sail eighty triremes through the back canals and attack the Egyptian rear. The Egyptians lost a Greek general in command of 5000 mercenaries and Nectanebos II withdrew to Memphis. Abandoned by Nectanebos, first the Greek garrison at Pelusium defected to the Persians, then one by one the cities of the Delta followed suit. Nectanebos, hearing that he had lost the Delta, gave up Egypt without further fight, fleeing with as much wealth as possible into exile in Ethiopia, where he was granted refuge. Artaxerxes III Ochus took the rest of Egypt without further difficulties. Nectanebos regained control of part of Upper Egypt, which he ruled down to 341 BCE, encouraging hopes that he would liberate all Egypt.
The native Egyptians suffered considerable reprisals under Artaxerxes III Ochus for their rebellion against Persian rule under Amyrtaeus in ca. 404 BCE. Temples were plundered. Ochus reputedly himself slew the Apis bull and the ram of Mendes, feasting on their flesh. In their place he required Egyptians to worship the ass, a sacred animal of Seth-Typhon, god of foreigners. Chafing under Persian rule, Egyptians gave credence to a subversive prophecy that Nectanebos II would return from Ethiopia, after an absence of 13 years (343-331 BCE), to overthrown the Persian oppressors and deliver the Egyptians. When Alexander the Great conquered Egypt in 332 BCE, he posed as its liberator from the Persians and benevolent successor to the pharaohs, participating in Egyptian rites honoring the Apis bull and other Egyptian gods, and visiting the oracle of Ammon at Siwa. The native population welcomed his "liberation" of Egypt from the Persians, and it appears that many accepted Alexander as the fulfillment of the Nectanebos prophecy, that is, as the liberator Nectanebos returned. The identification of Alexander with Nectanebos is documented in The Alexander Romance, the oldest parts of which were written not long after Alexander's conquest. The Alexander Romance recorded an interesting story in which Nectanebos fled Egypt to Macedonia where he secretly fathered Alexander the Great. Alexander, though seemingly a Greek conqueror, was in actuality— according to this legend—born an Egyptian prince. Philip of Macedon suspected the baby Alexander was not his and sought to slay him, but the gods saved the child. Due to the prodigies that accompanied Alexander's birth, Philip was convinced that the child was offspring of a god and raised him accordingly. Later, when Alexander conquered Egypt, he was shown the statue of Nectanebos that predicted Nectanebos's return as a young man. Alexander was publicly revealed as the son of Nectanebos—Nectanebos reincarnate—and the fulfillment of the Nectanebos Prophecy.Given the deliberate parallels the DH draws between Saul, David, and Solomon to Alexander, Ptolemy I and Ptolemy II, respectively, as well as the identification of David (Ptolemy I) as the rightful heir to Saul (Alexander) in God's eyes, the Ptolemies' resort to the Nectanebos prophecy seems like an obvious response.