Showjumper Athina Onassis has lost her top mare Ad Camille Z (pictured earlier this year), after the pair suffered a serious fall in Switzerland last night (Thursday 11 December).

Athina and Ad Camille Z were competing at the CHI Geneva horse show in the Credit Suisse Grand Prix when they fell at the eighth jump — an oxer.

The 29-year-old rider was unhurt by the fall, but the horse suffered a fatal injury, breaking her leg.

Ad Camille Z, an 11-year-old grey mare, was hoisted out of the arena by a crane and taken to veterinary hospital. It reportedly took 45 minutes to remove the horse from the arena. When she arrived at hospital her injuries were too severe and the horse was put down.

The class was delayed by an hour but continued, with American rider Lauren Hough and bay mare Ohlala taking top honours.

Germany’s Ludger Beerbaum was second with Chaman, with Pieter Devo and Dream of India Greenfield third and Ireland’s Bertram Allen and Molly Malone V fourth.

Athina and Ad Camille Z had been out competing frequently this year, most recently at the Gucci Paris Masters. They also took part in the Global Champions Tour, in which Athina finished 13th in the 2014 rankings accruing €60,135 in prize money.

Heiress Athina, who is the only granddaughter of shipping tycoon Aristotle Onassis, is married Brazilian showjumper Alvaro de Miranda Neto, more commonly known as Doda. The pair live in Brazil and the Rio De Janeiro leg of the Global Champions tour is named after her — the Athina Onassis International Horse Show.

In 2012 Athina suffered a serious injury herself in a fall, fracturing two vertebrae in her neck. She made a full recovery.