Charles Ellicott Commentary 2 Chronicles 20:31

"And Jehoshaphat reigned over Judah: he was thirty and five years old when he began to reign; and he reigned twenty and five years in Jerusalem: and his mother`s name was Azubah the daughter of Shilhi." — 2 Chronicles 20:31 (ASV)

CONCLUDING NOTICES. END OF THE REIGN
(2 Chronicles 20:31 – 21:1).

Compare 1 Kings 22:41–50. A brief section, which constitutes the whole account of the reign of Jehoshaphat in the older narrative.

And Jehoshaphat reigned over Judah. —Kings adds: “In the fourth year of Ahab king of Israel.” With this omission, our verse coincides with 1 Kings 22:41–42.