Ken Flach, who won four Grand Slam titles in men's doubles and two in mixed doubles, has died, according to the ATP World Tour and International Tennis Federation. He was 54.
The ATP World Tour announced Tuesday that Flach died Monday night in California after a brief illness.
In a posting on Facebook, Flach's widow, Christina, wrote that he "passed away after fighting pneumonia."
"Ken was taken far too soon and his sudden passing comes as a real shock to everyone in tennis," ATP President Chris Kermode said, adding that Flach "will be remembered as one of the great U.S. doubles players in the history of our sport."
Flach was remembered Tuesday on the main stadium court at the BNP Paribas Open in Indian Wells, California. His picture was shown on the video board and the announcer mentioned his career highlights.