"It was actually heartbreaking as everyone thought he was going to die."
This all happened when the duo were well on track for qualifying for the Olympics with wins right across the dressage board.
Luckily JHT Antonello bounced back with remarkable timing and after just two weeks of training won nationals before being crowned dressage champion at HOY.
"Not long after that we qualified for the Olympics over in Melbourne. We were just so lucky, it was amazing."
Since then the pair haven't dropped scores in the dressage arena below 70 per cent and they are now ranked 99th in the world.
This doesn't come easy for Mr Thompson as six days a week they are out in the paddock training.
"It's such a journey as its not just you, you have a partner. Building a relationship and having good communication is vital. When we do well together it is so fulfilling."
Right before they enter the arena Mr Thompson said he works to keep his mind in the present and block out any other external thoughts.
He described himself as an over thinker so said the challenge was to channel that intensity without those un-needed thoughts.
JHT Antonello is a strong-willed horse who is known for is attitude but Mr Thompson said through their training he has managed to pull him in to line.
"Although it is safe to say I don't always win with him but luckily we pull through in the end and work well together."
Alongside his own training Mr Thompson trains the New Zealand High Performance Young Riders.
He said it was great to pass on his own experience and knowledge to the up and coming.
"It is interesting to see the talent coming through and putting work in to what should be our future stars. I have a real passion for teaching."
Mr Thompson takes to the arena tomorrow with the first round kicking off at 3:15pm.
The second round then takes place on Saturday and on Sunday the champion is announced after the third round.
"I am a show pony at heart so cannot wait to get in to the ring and turn it on."