Khun Worawongsathirat (Thai: วรวงศาธิราช) was a usurper in the Ayutthaya Kingdom, ruling for only 42 days in 1548 before being assassinated. Siamese chronicles relate that Worawongsathirat attainted the crown — his kingship is not accepted by most traditional historians.
His birth-name was "Bun Si" (or Bun Sri) (Thai: บุญศรี), and he was a Brahmin. Upon entering service to the crown as keeper of Ho Phra Thep Bidon (หอพระเทพบิดร), a cloister on the palace grounds (with duties such as organising various rites and ceremonies,) Bun Si was then styled Phan But Si Thep (พันบุตรศรีเทพ). He was later promoted to the rank of Khun and styled Khun Chinnarat (ขุนชินราช); this was perhaps even as he was having an adulterous affair with Si Suda Chan (or Sri Suda Chan ศรีสุดาจันทร์), a first-class concubine of King Chairachathirat.
Si Suda Chan was not a real name of a person, it was the title of one of the four first-class concubines, which were Insuren, Si Suda Chan, Inthrathewi and Si Chula Lak. The real name of King Chairachathirat's consort was not mentioned in the history.
King Chairachathirat died in 1546, possibly poisoned by her hand. Their young son, Phra Kaewfa, ascended the throne as King Yot Fa with his mother as regent. (Whether Si Suda Chan and Khun Chinnarat had their affair before or after the ascension of Yot Fa is subject to debate. Jeremias van Vliet's memories told that they met after the coronation of Yot Fa which contrasted to those of Fernão Mendes Pinto.)
In 1548, Yot Fa was killed and Si Suda Chan, still acting as a regent, put Khun Chinnarat on the throne styled "Khun Worawongsathirat". Traditional historians criticise this usurpation as a great violation of morality. Some modern historians, however, take an alternative view. In this interpretation, Si Suda Chan, being of the deposed House of Uthong, intended to restore it to the Ayutthayan throne; and that Bun Si was also of the Uthong clan. Thus Worawongsethirat's reign could be called a restoration of the Uthong clan to Ayutthayan authority, at the expense of the House of Suphannaphum and other noble clans.
Those of the Suphannaphum clan responded by forming alliances with the Sukhothai clan led by Khun Phirenthorathep and Si Thammasok, and of the Nakhon Si Thammarat clan led by Khun Intharathep. Their plot to overthrow Worawongsathirat involved the discovery of a white elephant (pachyderm) in Lop Buri in 1548. White elephants are considered sacred and symbols of royal power; all those discovered are normally presented to the king. The king was told that mahouts were unable to tame the elephant, so the king was invited to go tame it, himself. On setting out by royal barge along Pla Mo Canal (Thai: คลองปลาหมอ), beside Sa Bua Canal (Thai: คลองสระบัว) (historian Jeremias van Vliet says it was on the side nearer the Palace Gate) Worawongsathirat was killed by gunshot. His head and that of his paramour were then displayed on spikes, and their bodies left to vultures. Those executing the coup then gave the throne to Prince Thian Racha, styled Mahachakkraphat.