This morning I came across a reference to the time of the kings in Israel in, get this: the book of Genesis! 

“These are the kings who reigned in the land of Edom, before any king reigned over the Israelites.” (Genesis 36:31 ESV)

Rushdoony explains, 

“Edom developed a monarchy very early in its history. In. v. 31, a note tells us that, long before the days of Saul, there was a monarchy in Edom. This note was added by one of the prophets, as a custodian of God’s word, perhaps Samuel.”

Excerpt From: R. J. Rushdoony. “Genesis: Commentaries on the Pentateuch Vol. 1.” Apple Books. 

but perhaps Keil & Delitzsch understand it best, as they state it in terms of prophecy, for Moses was indeed a promise. Delitzsch writes:

“as written with the promise in mind, that kings should come out of the loins of Jacob (Gen. 35:11, cf. 17:4ff.), and merely expresses the thought, that Edom became a kingdom at an earlier period than Israel. Such a thought was by no means inappropriate to the Mosaic age. For the idea, “that Israel was destined to grow into a kingdom with monarchs of his own family, was a hope handed down to the age of Moses, which the long residence in Egypt was well adapted to foster” (Del. ).”

Since “Genesis was written after the Exodus (ca. 1445 B.C.), but before Moses’ death (ca. 1405 B.C.)” (MacArthur), and “Kings was written between 561–538 B.C.” (Ibid.), the above explanations are plausible, but I take the second to be more acceptable since Moses was a prophet entirely capable of speaking of the time of the kings to come. He did the same in predicting the Exodus as God gave him. Nonetheless, since it is not explicit as the aforementioned reference to Moses’ predication of the Exodus, there is possibility that Samuel as a custodian fo the Pentateuch did add certain items including the recording of Moses death. But still, my conviction based on the fact that Moses wrote the Pentateuch in Jesus’ eyes, is that Moses actually predicted the time of the kings. Work out your own salvation with fear and trembling, but that is as far as I studied the matter this morning and it was a helpful exercise.