A dentist in Taiwan has been ordered to pay his mother over $750,000 (NT$22.33 million) for school fees after the country’s supreme court ruled that he must honour a contract signed 20 years ago.

The man, who is identified as Chu in court papers, signed the document in 1997. Under the agreement, Chu said he would pay 60 percent of his monthly income to his mother after he qualified as a dentist, Taiwan News reports.

Chu would then pay his mother, Lou, the sum every month until he paid back $844,400 (NT$25 million). The figure was supposed to cover her costs and included extra money to repay her for her efforts.

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After she entered into an identical arrangement with her other son, Lou said she accrued a debt of more than $675,600 (NT$20 million) putting them through college after she divorced from her husband. Under Taiwanese law people are required to provide for their elderly parents, failing to do so can result in a fine and even a spell in prison.

Chu, who has been practising dentistry since 2003, said he was only 20 when he entered into the agreement and argued that the contract should be declared invalid because it violates good customs and social morals.

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However, after a hotly contested courtroom battle, Taiwan’s supreme court found in favor of his mother. The court said that repaying the money will not cause him to struggle for survival and, after deducting payments already made, ordered him to pay his mother NT$22.33 million ($750,000).