: "Unfortunately we have a problem with Altior. It was discovered on Saturday morning that he was suffering from a severe bout of colic.
"As a consequence, he was taken to the equine hospital very very quickly where he had to undergo a four hour operation to remove a considerable amount of his intestine.
"It was a big operation and not straightforward.On Sunday morning, he was still extremely uncomfortable so had to undergo further surgery due to complications.
"There is some reasonably positive news in the fact that this morning he is stable, but still critical.
"Pat Pugh has been to see him on several occasions and he is currently in extremely good hands with all of the team at Donnington Valley.
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"It’s a terrible shame because he deserves a long and happy retirement and was really enjoying life at Chloe and Mick Fitzgerald’s.
"It’s been extremely tough, and no horse deserves this, especially dear Altior who gave so much pleasure to everyone on the track."
Altior was a four-time Cheltenham Festival winner and won 21 of his 26 races, amassing a staggering £1.3million in career earnings.
His last win was a Grade 2 Chase at Newbury in February 2020.
What is colic?
Colic is a term used to describe tummy pain in a horse, usually caused by an issue with their intestines.
Symptoms can show in many forms and the illness can be mild or life-threatening.
Colic is unpredictable and horses are naturally prone to it.
But it was for his Festival heroics that fans cherish him the most.
They formed part of an incredible 19-race winning streak and, in addition to the Champion Chase wins, included the 2017 Arkle and 2016 Supreme.
Henderson, who has huge 1-4 Champion Hurdle fav Constitution Hill this year, added: "In an ironic twist, we welcomed Altior's gorgeous four-year-old brother to Seven Barrows last week.
"He is the most handsome son of Camelot and is really pleasing us all.
"We are all praying and doing everything humanely possible to ensure Altior can pull through and continue living life as he should."
Punters were quick to send well wishes to the horse and those associated with him.
One said: "Let's have one more win, please, Altior!"
Another wrote: "Just seen the news on Altior. Hoping and praying the old boy pulls through."
While one comment read: "He always dug deep in a battle on the track, let's hope he can show the same spirit against this!"
It has already been a sad week for racing.
Hugely popular trainer Milton Bradley passed away aged 88, with the sport paying tribute to a 'great man'.