King from the House of Dovid

בראשית מט, י לֹּא-יָסו ר שׁ ֵּבֶט מִיהו דָה

ירושלמי מסכת סוטה דף לז/א פרק ח הלכה ג אין מושחין כהנים מלכים. אמר רבי יודן ענתונדריה על שם (בראשית מט) לא יסור שבט מיהודה.

Optimally, a king is appointed from the House of Dovid. However, if no fitting candidate exists from the House of Dovid, or for other reasons, a King may be appointed from another tribe. However such a King does not cause to inherit the Kingship to his children and he is also not anointed with oil. The Gemura’s citing of the Cohanim teaches that one might have thought that the Cohanim are very spiritual and already have leadership qualities, nevertheless, if a Cohen becomes a king, not being from the House of Dovid, he would not be anointed.