Now the rest of the acts of Jehoshaphat, from first to last, are written in the chronicles of Jehu the son of Hanani, which are recorded in the Book of the Kings of Israel.
We are now drawing towards the close of the history of Jehoshaphat's reign, for a further account of which those who lived when this book was published were referred to an authentic history of it, written by Jehu the prophet (Ch2 19:2), which was then extant, Ch2 20:34.
Commenting on 2 Chronicles 20:31-37
And after this did Jehoshaphat king of Judah join himself with Ahaziah king of Israel,.... Meaning, not after the invasion of the Moabites, &c. and the slaughter of them, but after Jehoshaphat returned from Ramothgilead, when he was reproved by a prophet for helping the ungodly, Ch2 19:1 so that it was a great aggravation of his folly and weakness, that after that, and quickly...
In the book of Jehu - This is totally lost, though it is evident that it was in being when the books of Chronicles were written.