Thailand's royalty made an unprecedented move into politics Friday when the sister of King Maha Vajiralongkorn was declared a prime ministerial candidate in a March 24 general election, registration papers showed.

The nomination of Princess Ubolratana Rajakanya Sirivadhana Barnavadi, 67, the elder sister of King Maha Vajiralongkorn, promises to upend Thailand's already turbulent politics because it breaks the long-standing tradition of royalty staying out of politics.

Ubolratana will run as a candidate for a party loyal to ousted Prime Minister Thaksin Shinawatra. One of her leading opponents will be Prime Minister Prayuth Chan-ocha, the leader of the military junta, who also announced his candidacy Friday.