The particular hierarchy of rank and title is unique to Thailand, although a similar, but less complex system exists within the royal family of Cambodia, Thailand has the most elaborate system of royal rank in any country in the world. There are three distinct ranks of Prince and Princess, but even within each rank there are finer distinctions which divide the members into different sub-groups. The three ranks are as follows:
The Chao Fa: This title is usually restricted to the children of a King or Queen. There are at present only five Chao Fa living, one Prince and four Princesses;
The Phra Ong Chao: There are two specific grades within this rank, those Phra Ong Chao who have the additional word Chao within the preamble to their title, and those who do not: (Phra Chao Vorawongse Ther) Phra Ong Chao - Prince or Princess and Royal Highness. (Phra Vorawongse Ther) Phra Ong Chao - Prince or Princess and Highness. Today the Phra Ong Chao are always the grand children of a king.
The Mom Chao: This is lowest of the royal ranks and the usual title of a grandchild of a King (except where raised to be a Phra Ong Chao); in the case of a great - grandchild of a King who is a Mom Chao then he or she is the child of a Phra Ong Chao Prince, who is himself of a grandchild of a King.
Mom Rajawongse: The great - grandchildren of a King do not bear royal rank but are entitled to use the title of Mom Rajawongse, which is not translated into English. The great-great - grandchildren bear the title of Mom Luang. Subsequent generations in the male line of descent from a King have no titles, but may add the dynastic surname such as, "na Ayudhya" as used in the Chakri Dynastic family, from whence the Royal Chakri Family was first founded, to the surname of the branch of Royal Family from which they descend.