הָעֲשִׂירִ֣י שִׁמְעִ֔י בָּנָ֥יו וְאֶחָ֖יו שְׁנֵ֥ים עָשָֽׂר׃
Le dixième fut Chimeï; avec ses fils et ses frères, douze.
Rashi
and Mattithiah - six But you will find only five. [The answer is that] his wife was pregnant with Shimei, and he saw through the holy spirit that he too was destined to be the chief of a watch; therefore he says “six.” And that is what is stated further: (verse 17): “The tenth: Shimei.” This is what the liturgical poet set down (in the Kedushah of Yozer of Parashath Shekalim): “Inscribed from the womb to be counted in the watch of the Sanctuary.”