CHAMPION trainer Paul Nicholls hailed Kauto Star a "once in a lifetime" horse after the dual Cheltenham Gold Cup winner had to be put down due to injuries sustained in a paddock accident.

The 15-year-old enjoyed a glittering career with the champion trainer after being bought from France as a four-year-old, most notably winning the King George VI Chase at Kempton five times and becoming the first horse to regain the Cheltenham Gold Cup.

He retired from racing after pulling up in the 2012 renewal of the blue riband having won 23 of his 41 races and over £2.3million in win and place prize-money.

Later that year Kauto Star went on to pursue a career in dressage with Laura Collett, a decision which led to a breakdown in relations between Nicholls and owner Clive Smith.

Nicholls said: "It's obviously a very sad day and very sad news to take on board. I'm obviously mortified.

"He was like my best mate really. I saw him every day and he was a great horse in every way temperament-wise."

Kauto Star looked as though his best days could be behind him after pulling up in the 2011 Punchestown Gold Cup, but famously roared back later that year to win a fourth Betfair Chase at Haydock and his fifth King George VI Chase, days Nicholls admits were particularly special.

He said: "He won 16 Grade Ones. I've been very lucky to have trained some incredible horses, but I've always said he's once in a lifetime."

Mr Smith explained Kauto Star had suffered what appeared to be a minor injury last week but his condition deteriorated over the weekend.

He said: "I am devastated. He had been turned out in Laura's paddock, as has been the case normally with him at this time for years, and he looks to have jumped something, and perhaps stumbled, we're not really sure, but he injured himself - and it became obvious it was serious.

"The vets at Valley Equine Hospital (in Lambourn) did all they could but it became increasingly apparent the injuries were too serious and that it was in the horse's interests to be put down."

Ruby Walsh steered Kauto Star to 17 of his 19 victories in Britain and Ireland combined and believes he should go down as one of the greatest National Hunt horses of all time.

He said: "Kauto Star was a superstar and it's a real shame that his life off the track has been cut short.

"He was a wonderful horse to ride and he gave me some of the best days I'll ever have as a jockey."