London 2012 gold medal winner Ben Maher is being sued for up to £700,000 amid claims he made secret profits from dealing in horses.
Maher, who won team gold at London 2012 alongside Scott Brash, Nick Skelton and Peter Charles, has had the action brought against him by his long-term backers Mike and Emma Phillips.
In his role as a bloodstock agent for the couple, Maher is alleged to have quoted incorrect prices on horse sales to the Phillips, and pocketed the difference.
The couple have worked with the rider since he was 22 and are said to be disillusioned having treated him "as one of the family".
"It is all now in the hands of the court. It's a very sad end to a highly successful partnership," said Emma.
The case will be heard at the Chancery Division of the High Court, with Maher expected to strenuously deny the allegations against him.
Court papers claim that Maher made secret profit on six horses in total, with the rider allegedly having siphoned off $350,000 from the sale of one horse, Tackeray.
The papers claim that Maher negotiated a sale of Tackeray to American owners for $850,000 but informed his backers that the sale was in fact for the smaller sum of $500,000.
"Mr Maher thereby made a secret profit of $350,000 of which Mr Maher is accountable and to which Quainton Stud is entitled," says the court document.
He is also accused of making a profit on another five other horses: Quainton Quirifino (10,000 euros), Awanti (50,000 euros), Vigolo (126,000 euros), Robin Hood (£80,000) and Wonderboy (£222,496).
In current conversion rates, the total amounts to nearly £700,000, but the financial ramifications could be far greater – as he could incur costs and damages in the event of losing the case.
"We did all we could to provide the conditions that led to Ben's fantastic success at the Olympics last year and now feel broken-hearted," said Emma.
As part of the civil action, the Phillips are requesting that Maher sells part of his stake in his Olympic medal winning horse, Tripple X.