Which crown prince had an affair with his father's concubine, was deposed, and imprisoned?

Extravagance and decadence

During the reign of King Ly Cao Tong, the government was severely weakened, and rebellions broke out everywhere due to the extravagance and debauchery of the head of the court. The Complete Annals of Dai Viet recorded that "the king indulged in excessive revelry, administration was unclear, bandits rose up like swarms of bees, and famine lasted for years."
The book "Vietnamese History in Brief" records that the king "was very greedy for wealth and profit, making the selling of official positions and the trading of prisons his main business." Whenever there was a lawsuit, the king would often take advantage of it, so "the state's treasury was overflowing with wealth like mountains, while the people complained and grumbled. Bandits and robbers rose up like swarms of bees."
King Lý Cao Tông was fond of revelry, traveling, and feasting. “The king often went outside the Hải Thanh palace. Every night he would order musicians to play the Bà Lỗ lute and sing songs in the Champa style, the music sounding mournful and heart-wrenching. Those listening were moved to tears. The monk Nguyễn Thường said to the king, ‘I see in the preface to the Book of Songs: The music of a country in turmoil sounds like sorrow and longing, because the people of that country are suffering. Now, Your Majesty indulges in excessive pleasure, your governance and education are flawed and scattered, causing the common people to suffer greatly. And today, hearing such mournful music , isn’t that a sign of national turmoil and ruin?’”
In 1203, Emperor Gaozong also had a series of palaces and terraces built in front of the capital. Even during the most turbulent years, when roads were congested, the emperor still liked to wander around, but couldn't go anywhere. So he ordered the construction of the Ung Phong and Hai Thanh royal residences, where every day he would have his courtiers, palace maids, and theatrical troupes row small boats as a royal procession, as if he were going on a pleasure trip. Then he ordered beeswax to wrap silk and various seafood items in a pond and release them, then had people wade in to retrieve them, pretending they were objects from the imperial palace, to offer as gifts…

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