A Vietnamese Royal Wife Swap

In the 13th century Emperor Ly Hue Tong of Vietnam (1194–1226) had married a beautiful relative of Tran Thu Do (1194–1264). After Hue Tong’s accession, Tran Thu Do became his all-powerful grand chancellor, and further secured his position by marrying 2 of his nephews to the daughters of Hue Tong. 

Emperor Hue Tong suffered increasingly from mental problems. In 1224 he was forced to abdicate in favour of his youngest, 6-year-old daughter, Chiêu Hoàng (1218-78). Soon afterwards, the young Empress was forced to abdicate in favour of her husband, Tran Thái Tông (1218-77). In 1226 ex-Emperor Hue Tong was forced to commit suicide.

When the teenage Empress Chiêu Hoàng did not give birth to a son for some time, the all-powerful Tran Thu Do became worried. In 1237 he forced his eldest nephew, Tran Liêu (1211–51), to give up his 3-months pregnant Royal wife, Thuân Thiên (Chiêu Hoàng’s elder sister), to his younger brother, the Emperor Tran Thái Tông. Tran Thái Tông’s wife and Empress, Chiêu Hoàng, was downgraded to Princess, when her pregnant elder sister, Thuân Thiên (1216–1248), took her place.

Furious at losing his pregnant royal wife, Tran Liêu rose in revolt, while Tran Thái Tông felt so awkward about the situation that he wanted to become a monk. Tran Thu Do, however, succeeded in persuading Tran Thái Tông to return to the throne, while he forced Tran Liêu to surrender. Tran Thu Do wanted to behead his rebellious nephew, but was stopped by Tran Thái Tông.

The new Empress, Thuân Thiên, subsequently gave birth a Prince. Apperently, her younger sister, the former Empress Chiêu Thánh, too, was at first married to her brother-in-law, Thuân Thiên's ex, but in 1258 Chiêu Thánh was married to general Lê Phu Trân. She had 2 children with him.