BANGKOK — The sister of Thailand’s king was nominated on Friday as a candidate for prime minister, but by day’s end, the political foray was rebuked by the monarch as “inappropriate” behavior that violated the nation’s constitutional monarchy, apparently ending her candidacy.

In a kingdom where the royal family is considered above the volcanic eruptions of Thai politics, the prospect of the king’s sister running for office, followed by the public airing of a disagreement between the royal siblings, upended the political landscape.

Ubolratana Rajakanya Sirivadhana Varnavadi, 67, the elder sister of King Maha Vajiralongkorn Bodindradebayavarangkun, was nominated by a party associated with the Shinawatra political family, which includes two fugitive former prime ministers who have been accused of subverting the power of Thailand’s royal institutions.

Calling Ms. Ubolratana “an educated and skilled person” who was the “most suitable choice,” Preechapol Pongpanich, the leader of the Thai Raksa Chart Party, announced her candidacy on Friday but cautioned that the choice still had to be accepted by Thailand’s election commission.