China’s sovereign-wealth fund has sold out of its stake in Blackstone Group LP, ending a longstanding relationship with the private-equity giant at a time of growing tensions between the U.S. and China.

The sale marks a reversal for one of China’s most-scrutinised investments from the pre-crisis era, a purchase that, to many observers, marked a watershed in China’s growth from an up-and-coming emerging-market economy to a true global giant with deepening relationships on Wall Street and across Europe.