Ginny Howe and Cavort at Badminton earlier this year.
The 13-year-old son of Cavalier Royal and Mystery Queen broke his shoulder in a fall at the 13th obstacle, the HSBC Corners.
Howe's family bought Cavort in 2006, with Ginny taking over the ride on the 17.1hh bay gelding from Christopher Toms, who took the horse up to Advanced level.
Howe and Cavort represented Great Britain as individuals at the 2007 European Young Riders Championships.
Cavort had a consistent record at three-star level and the combination's first international four-star was Pau in France last October. They completed Badminton in May. Cavort had 150 British Eventing points.
Howe paid tribute to Cavort on her website. "We will all miss you in our lives, but no one more than me. We formed a partnership that will never be replaced. You taught me so much and we achieved so much together, I adore you and even in your last moments you made sure I was safe ... I thank you for that."