Princess Maha Chakri Sirindhorn[1] (Thai: มหาจักรีสิรินธร, Thai pronunciation: [má.hǎː .ʨàk.krīː.sì.rīn.tʰɔːn]; rtgs: Maha Chakkri Sirinthon; born 2 April 1955) is the second daughter of King Bhumibol Adulyadej.
Her full ceremonial title is Somdech Phra Debaratanarajasuda Chao Fa Maha Chakri Sirindhorn Rathasimagunakornpiyajat Sayamboromrajakumari [2] (สมเด็จพระเทพรัตนราชสุดา เจ้าฟ้ามหาจักรีสิรินธร รัฐสีมาคุณากรปิยชาติ สยามบรมราชกุมารี; rtgs: Somdet Phra Theppha Rat Rat Suda Chao Fa Maha Chakkri Sirinthon Rattha Sima Khuna Kon Piya Chat Sayam Boromma Ratcha Kumari), which was bestowed upon her on 5 December 1977. Thais commonly refer to her by reducing such title to “Phra Thep”, meaning "princess angel". Her title in Thai is the female equivalent of the title held by her brother, Crown Prince Maha Vajiralongkorn.[3] The Thai constitution was altered in 1974 to allow for female succession, thus making her eligible for the throne.[4]
As the eldest female child of the royal family (excluding Ubol Ratana, who married a foreign commoner), her position is comparable to a princess royal.[5]