Organisers have cancelled this year's Mitsubishi Motors Badminton Horse Trials after they accepted there was "no chance" of the ground drying out in time.
The most prestigious four-star competition in world eventing was due to start on Friday with two days of dressage, followed by cross-country on Sunday and Monday's showjumping finale.
It had been given added significance this year by Britain's world number one William Fox-Pitt going for the £220,000 Rolex Grand Slam, a prize awarded for any rider that wins consecutive Burghley, Kentucky and Badminton titles.
Fox-Pitt last night added the Kentucky crown to his Burghley victory seven months ago - both aboard Parklane Hawk - but his Badminton hopes have now been dashed.
"The recent exceptional rainfall has left the ground at Badminton totally waterlogged and partially flooded," Badminton director Hugh Thomas said.
"Further rain is due this week, leaving no chance of the ground drying out.
"Very sadly, therefore, the 2012 Mitsubishi Motors Badminton Horse Trials has been cancelled.
"Purchasers of advance tickets, exhibitors, sponsors and riders will of course be refunded as soon as is practical."
The event will not be rescheduled, with today's announcement confirming the first cancellation since 1987. It was also called off in 1975, 1966 and 1963.
The news is no great surprise, though, given the weather conditions. Reigning Badminton champion Mark Todd Tweeted last night: "Not liking the look of the weather forecast for this week - not at all."
But it is a major blow to the sport, given the huge crowds that Badminton attracts, especially on cross-country day.
This year's competition would have seen a Badminton debut for Germany's Michael Jung, the current world and European champion, in addition to Todd defending his title and Fox-Pitt spearheading a powerful British challenge.
It is also comes as a setback for the British selectors three months before London 2012, although most of the top riders were not entered at Badminton on their potential Olympic horses.
Britain will send a team of five to London, with Fox-Pitt, Mary King, Piggy French and Nicola Wilson seemingly having nailed down four of those places.
The fifth spot, though, remains wide open, and attention will now switch to Chatsworth Horse Trials in Derbyshire from May 11-13, where several possible Olympic combinations are due to compete.