Princess Apolratana Rajakania Serivadhana Barnavady (67 years) is the king's great sister and will be the reason for the royal family to enter politics.
Abolratana relinquished her royal titles in 1972 when she married American Peter Jensen, a fellow at the Massachusetts Institute of Technology. She lived in the United States for over 26 years until her divorce in 1998.
The leader of the Reform Party, Bayonne Nititown, a pro-army, said the nomination of the king's elder sister to the post could violate the election laws and demanded in a letter to the election commission to take a decision to invalidate the nomination.
He stressed that her candidacy violates a law that prevents political parties from using the monarchy in campaigning. Abulratana will be nominated by a party loyal to ousted Prime Minister Thaksin Shinawatra.
One of its main rivals in the election was Prime Minister Bariot Chan Ocha, a former army commander who announced on Friday the election.