Thawisan Ladawan (Thai: ทวีสันต์ ลดาวัลย์) (26 January 1923 – 7 April 2006) was husband of Busba Kitiyakara (younger sister of Queen Sirikit), a member of King Bhumibol Adulyadej's Privy Council, and for 26 years, principal private secretary to the King. Thawisan attended Vajiravudh College and graduated from the inaugural class of Thammasat University in 1938. He worked in several capitals, including Paris and Brussels, and earned a Diplome d'Etudes Superieures de Droit International Public from Paris University in 1954. He became Deputy Director-Deneral of the Protocol Department before departing in 1968 to serve as Deputy Principal Private Secretary to Bhumibol. A year later he became Bhumibol's Principal Private Secretary, and was later appointed to the Privy Council. He died at the age of 83 due to chronic liver disease.
Thawisan was the son of Phraphum Phichai (Mom Ratchawong Bung Ladawan) and Nuang Bunnag. His father was the prince of Chaiyaphum, Lamphun, Mae Hong Son, and Kamphaengphet.
Thawisan married Busaba Kittiyakara in 1958. They had a daughter, Suthawan Ladawan Sathirathai on 24 September 1958. He divorced her soon afterwards and never remarried. Suthawan married Surakiart Sathirathai.