Tu Duc (1829-1883), who was the last of the pre-French emperors of Vietnam, signed a treaty in 1861 giving the French control of that country. He was the fourth of the 13 Nguyen Dynasty emperors. That dynasty was created by Nguyen Anh, who, with French assistance, named himself Emperor Gia Long (1802-1820), starting the Nguyen Dynasty and established his capital at Hue. The French, therefore, were not a new experience to Tu Duc. 
Tu Duc, known as a scholar and patron of Vietnamese culture. according to Pham Cao Duong (Encyclopedia of the Vietnam War: A Political, Social, and Military History, page 706) was independent Vietnam's last emperor, 1847-1883. Some would perhaps regard him as the emperor who lost Vietnam to French domination.
French incursions into Vietnam began at the beginning of his reign, with a naval expedition in 1857, and a major French fleet, in 1861, reinforced Gia Dinh (i.e., Saigon) and gained control of the surrounding provinces.
The June 1862 Treaty of Saigon transferred the three provinces surrounding Sagon to France, opening of three ports to trade, allowing free passage of French warships on the Mekong River and freedom of action for French missionary, and reimbursing France for its losses in the attack. 
Tu Duc apparently felt too isolated from popular support to rise against the French. He thought he might, by these concessions, free his troops to suppress a Christian-supported in Bac Bo, which, indeed, he put down in 1865. His forces killed many Christians, and, in retrospect, the need to save souls was merely a French government excuse for intervention.
French missionaries, who had urged their government to support this rebellion, were disillusioned when it did not, especially after thousands of Christians were slaughtered by Tu Duc's forces following the rebellion. The missionaries, however, had served only as an initial excuse for French intervention in Vietnam; military and economic interests soon became the primary reasons for remaining there. Additional treaties turned Vietnam into a French protectorate when Tu Duc died in 1884. Tu Duc had had no heirs. 
- , Vietnamese Independence (950 - 1859)"History of Vietnam", Windows on Asia
- Bolt, Ernest C. Jr., (Fall 2001), Major Early Nguyen Emperors: Emperor Tu Duc, HISTORY 398: Special Topics: The United States and Cuba: Readings in Diplomatic, Economic, and Social Connections, University of Richmond
- Cima, Ronald J., ed. (1987.), Under French Rule, Vietnam: A Country Study, Library of Congress