Nov 2 (Reuters) - BlackRock is preparing to sell a portion of its investment in British e-commerce group THG , a bookrunner for the deal said on Tuesday, at a discount to the stock’s last closing price. BlackRock’s planned sale of 58 million THG shares was priced at 195 pence per share, Goldman Sachs said, which implies a 10.3% discount to the stock’s Monday close. The U.S. asset manager is THG’s biggest institutional shareholder with a 10.13% stake of nearly 124 million shares, according to Refinitiv data. (Reporting by Sachin Ravikumar in Bengaluru; Editing by Ramakrishnan M.)