Gordon Elliott has said he wishes to 'apologise profoundly' after an investigation was launched into an image of the leading trainer which was posted on social media on Saturday.
The image was posted and widely shared on Twitter, with the regulatory board (Irish Horseracing Regulatory Board) of the sport in Ireland later tweeting: "The IHRB are aware of an image circulating on social media and the matter is under investigation."
The image appears to show Elliott sitting on a dead horse on the gallops.
In a statement, the trainer said: "I would like to address the speculation and rumours that have been rife since an old photo of me began circulating on social media yesterday afternoon.
"Firstly, I apologise profoundly for any offence that this photo has caused and can categorically state that the welfare of each and every horse under my care is paramount and has been central to the success that we have enjoyed here at Cullentra.
"The photo in question was taken some time ago and occurred after a horse had died of an apparent heart attack on the gallops. I appreciate that an initial viewing of this photo suggests it is a callous and staged photo but nothing could be further from the truth.
"At what was a sad time, which it is when any horse under my care passes away, my initial reaction was to get the body removed from where it was positioned.
"I was standing over the horse waiting to help with the removal of the body, in the course of which, to my memory I received a call and, without thinking, I sat down to take it. Hearing a shout from one of my team, I gestured to wait until I was finished.
"Such background information may seem trivial at this time and will not allay the concerns of many people both within and outside the world of horse racing.
"However, I feel it is important to provide people with some context surrounding this photo. To the racing community, to anyone who has worked with and loves horses and to anyone offended by this image I cannot apologise enough.
"Horse welfare and the care and attention to detail involved is absolutely at the core of everything we do here and both myself and all of my team pride ourselves on those standards.
"Again I apologise for any offence caused and ask people to consider this statement as opposed to the various falsehoods and misinformation being circulated on social media.
"At this time, I would like to stress that I continue to extend my full cooperation with the ongoing IHRB investigation."
Speaking on Sunday lunchtime, an IHRB spokesman said: "The investigation is under way, and it will be dealt with as quickly as possible."
Elliott is a three-time Grand National winner, having sent out Silver Birch to claim the Aintree prize before Tiger Roll became the first back-to-back winner of the race since Red Rum when lifting the marathon event in 2018 and 2019.
The County Meath handler also counts 2016 Cheltenham Gold Cup hero Don Cossack among the best horses he has trained, with 32 Cheltenham Festival wins to his name so far.
Elliott houses a number of favourites for this year's Festival, including Envoi Allen and Zanahiyr, while Tiger Roll himself is also due to run in the Glenfarclas Chase over Cheltenham's cross-country fences.
The British Horseracing Authority has welcomed the IHRB's investigation, and is hoping for a speedy resolution.
A spokesperson said: "We hope the Irish authorities will quickly confirm how this shocking picture originated.
"Respect for horses is a fundamental value of our sport, contrary to the impression in this picture. The IHRB have assured us that the investigation will be carried out as quickly as possible and that they will keep us informed as more information becomes available."