Emperor Duy Tân (born Nguyễn Phúc Vĩnh San; 19 September 1900 – 26 December 1945), was a boy emperor of the Nguyễn Dynasty and reigned for 9 years between 1907 and 1916.

Duy Tân (at the time, known by his birth name, Prince Nguyễn Phúc Vĩnh San) was son of the Thành Thái emperor. Because of his opposition to French rule and his erratic, depraved actions (which some speculate were feigned to shield his opposition from the French) Thành Thái was declared insane and exiled to Vũng Tàu in 1907. The French decided to pass the throne to his son Nguyễn Phúc Vĩnh San, despite the fact that he was only seven years old. The French hoped that someone so young would be easily influenced and controlled, and thus raised to be pro-French.

The efforts on the part of the French to raise the prince to support them largely failed. Nguyễn Phúc Vĩnh San was enthroned with the reign name of Duy Tân, meaning "friend of reform", but in time he proved incapable of living up to this name. As he became older he noticed that, even though he was treated as the emperor, it was the colonial authorities who were actually obeyed. As he became a teenager, Emperor Duy Tân came under the influence of the mandarin Trần Cao Vân, who was very much opposed to the colonial administration. Emperor Duy Tân began to plan a secret rebellion with Trần Cao Vân and others to overthrow the French.

In 1916, while France was preoccupied with fighting World War I, Emperor Duy Tân was smuggled out of the Forbidden City with Trần Cao Vân to call upon the people to rise up against the French. However, the secret was revealed and France immediately sent troops there, and after only a few days, they were betrayed and captured by the French authorities. Because of his age and in order to avoid a worse situation, Emperor Duy Tân was deposed and exiled instead of being killed. Trần Cao Vân and the rest of the revolutionaries were all beheaded. Prince Nguyễn Phúc Vĩnh San was exiled with his father to Réunion Island in the Indian Ocean.

Prince Vĩnh San continued to favor national liberation for Vietnam in exile. During World War II he resisted the Vichy Regime until the Liberation of La Réunion, after which he joined the Free French Forces and became a low-ranking naval officer on the French destroyer Léopard, serving as radio officer. He then joined the Free French army as a second lieutenant in December 1942, receiving successive promotions to lieutenant (1943), captain (1944), major (July 1945) and lieutenant-colonel (September 1945).

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