The order of succession to the throne of Tonga is laid down in the 1875 constitution. The crown descends according to male-preference cognatic primogeniture. Only legitimate descendants through legitimate line of King George Tupou I's son and grandson, Crown Prince Tēvita ʻUnga and Prince ʻUelingatoni Ngū, are entitled to succeed. A person loses his or her right of succession and deprives his or her descendants of their right of succession if he or she marries without the monarch's permission.
Line of succession
The current line of succession is as follows:
References
Line of succession to the Tongan throne Wikipedia(Text) CC BY-SA