1 Kings 12:23

Speak unto Rehoboam the son of Solomon king of Judah
He is called king before, but of what tribe or tribes is not expressly said, only it is implied in ( 1 Kings 12:17 ) and he is only acknowledged king of Judah by the Lord himself:

and unto all the house of Judah and Benjamin;
which made but one house, as before but one tribe, ( 1 Kings 11:36 )

and to the remnant of the people;
of the other tribes that might dwell among them at Jerusalem, and especially Simeon, whose inheritance was within the tribe of Judah, ( Joshua 19:1 )

saying:
as follows.