Zhou Yongkang, China's former security chief, has been arrested and kicked out of the Communist Party, according to a Friday statement issued in Chinese by the official state news agency Xinhua. Zhou is charged with crimes including stealing state secrets, adultery and bribery. A formal corruption investigation has been launched against him by Supreme People's Procuratorate prosecutors, according to the BBC.

The four-month investigation into Zhou's conduct marks the highest-level Communist Party official to be probed for corruption under President Xi Jinping, who has made tackling public corruption a hallmark of the first two years of his presidency, Voice of America reported. The corruption investigation has also ensnared a number of relatives and associates of Zhou, a former Politburo Standing Committee member who has not been seen in more than a year, according to the BBC. 

Zhou, a 71-year-old who retired from his position as head of China's internal security system two years ago, allegedly engaged in "serious violations of party discipline," "accepting large sums of bribes," "disclosing party and state secrets" and "committing adultery with several women" in connection with corruption, the BBC quoted the Xinhua statement as saying.

Zhou was once the head of China's largest oil and gas company, China National Petroleum Corp., and was once seen as the country's third-most-powerful political leader, according to USA Today. The Politburo made the decision to expel Zhou during a meeting preceding the release of the Xinhua statement, and is sending the case on to "judicial organs" for a probable criminal trial, USA Today quoted the statement as saying. Zhou's oldest son has made more than $1 billion off public projects, according to Hong Kong tabloid Apple Daily, USA Today reported.