Zara Phillips was due to compete over the weekend
The Blenheim Palace International Horse Trials have been cancelled this weekend because of heavy rain.
The dressage stage took place on Friday, with Cumbrian Ruth Edge ahead on Mayhem III.
But the ground has been deemed unfit for the the planned cross-country and jumping phases on Saturday and Sunday.
It is the first time the event has been cancelled, and organisers said all people who have bought weekend tickets will be refunded.
"This is so disappointing because a huge amount of work has gone into the organisation of Blenheim," event director Mandy Hervieu said.
"The whole team has worked incredibly hard to cope with the conditions," she added.
"However, the safety of horses and riders is of paramount importance, plus vehicular access, and it was decided that the ground conditions could not ensure this."
Blenheim's host, The Duke of Marlborough, said: "It's so frustrating, because we were set for a great weekend with a terrific cross-country course."