“Now Rehoboam.” The text shifts from following the northern kingdom of Israel to the southern kingdom of Judah.
“Rehoboam was 41 years old when he began to reign.” The fact that Rehoboam was 41 when he became king the year Solomon died, and Solomon had reigned 40 years, means that Rehoboam was born before David died and Solomon became king. So Solomon already had at least one wife, Naamah, who was an Ammonite, before he married Pharaoh’s daughter (1 Kings 3:1).
“and his mother’s name was Naamah the Ammonite.” Naamah apparently had a very special relationship with Solomon, because she is the only wife of Solomon who is named in the Bible, and here in 1 Kings 14 she is listed twice (1 Kings 14:21, 31).
[For more information on Naamah, see commentary on 2 Chron. 12:13.]