 Complete the following phrase:  He has won four Grand Slam titles: one in mixed doubles at the 2011 US Open partnering Melanie Oudin, and three mens doubles titles at the 2014 Wimbledon Championships partnering Vasek Pospisil, and the 2018 Wimbledon Championships and 2018 US Open partnering Mike Bryan. He also won the 2018 ATP Finals mens doubles title partnering Mike Bryan. At the 2016 Rio Olympics, Sock won both a gold medal in mixed doubles partnering Bethanie Mattek-Sands, and a bronze medal in 