Bookmakers across the country have been celebrating after pocketing around £50m in bets after this weekend's Grand National race.
But the unlikely victory for 66/1 winner Auroras Encore has reportedly cost one £50,000.
Spread betting firm Sporting Index had initially predicted the race winner’s starting price would be between 18/1 and 20/1.
But when the horse - a 'skinner' at 66/1 - came in first, punters who bought that spread made 46 times their money.
When the horse - a 'skinner' at 66/1 - came in first, punters who bought that spread made 46 times their money
Auroras Encore and Ryan Mania after winning The John Smith's Grand National. The unlikely victory reportedly cost spread betting firm Sporting Index £50,000
Spread betting sees punters bet 'high or low' on a range of outcomes of an event.
The pay-off is based on the accuracy of the wager, rather than a simple 'win or lose' outcome.
A spread is a range of outcomes and the bet is whether the outcome will be above or below the spread.
The real loss for the bookmakers came because it also offered a bet multiplying the starting price by the margin of victory, offering a spread of 135-145.
As the horse was a 66/1 long shot and won by a comfortable nine lengths, some punters made 449 times their stake, with one landing £22,450 after buying the spread at £50 per point.
Wayne Lincoln, Sporting Index's trading spokesman, said it was 'highly unusual for a bookies to lose on the Grand National'.
The real loss for the bookmakers came because it also offered a bet multiplying the starting price by the margin of victory, offering a spread of 135-145
He added: 'Sporting Index are a spread betting firm that offer weird and wonderful markets on events like the Grand National.
'They're based a host of predictions and they challenge their clients to bet higher or lower on them
'We were predicting that the Grand National woulld be won by 20/1 shot.
'What has cost us a lot of money is that it was won by a 60/1 shot.
He said: 'The fixed-odds bookies couldn’t have wished for a better result, but Auroras Encore was an absolute nightmare for us.
He added: 'We were taken to the cleaners when Mon Mome won this race at 100/1 in 2009 and it’s a similar story this year.'
