This will be William's first World Equestrian Games after previously representing Great Britain at the European Championships in 2013 with Billy Buckingham's father, Billy Congo, where he was part of the gold medal-winning team.
Earlier this year William made history with Billy Buckingham becoming the fifth rider to record four wins in the Al shira'aa Derby at Hickstead.
The pair have made three Nations Cup appearances this year at Falsterbo, Hickstead and Dublin, helping to ensure Great Britain maintained their place in Europe Divison 1 for 2019.
2013 European Championships: Team Gold (Billy Congo)
2005 European Championships