A Malaysian royal’s plan to sell a tract of land in the heart of Singapore faces a complication: a tax bill that may exceed US$1 billion. A levy known as a land betterment charge has emerged as a sticking point in negotiations between some prospective buyers and the current owner, the eldest son of Malaysia’s billionaire king, according to people familiar with the matter. The owner wants any buyer to foot the bill, the people said, asking not to be identified because the information is...