"Unfortunately these things happen in racing and you just have to get on with it, but I'm just gutted for them as they are such nice people and he is such a good horse."
But he added: "I wouldn't be human if I didn't think it would give us a better chance.
"I'm delighted with my two, I couldn't be more pleased, but now it's just day to day with the race so close, and I hope they both get there now."
Kingscliff's big-race jockey Andrew Thornton was similarly sympathetic. He added: "It's one of those things. The race is going to be poorer for it."
Paul Nicholls, trainer of the new 11-2 second favourite with William Hill and Ladbrokes Strong Flow, knows all about the disappointment felt when a top-class horse is forced to miss out.
Strong Flow suffered a possible career-ending injury in 2003 when he cracked a bone in his knee. And the Ditcheat handler recently saw his well-fancied John Smith's Grand National hope Silver Birch ruled out the Aintree showpiece.
Nicholls said: "It shows what we are all up against at the moment when you've got all these nice horses getting ready for Cheltenham.
"Anything can happen and one feels for Hen and Terry (Biddlecombe) - they will be gutted.
"That's what happened to us with Silver Birch last week. These things do happen and we have to learn to live with it."
Best Mate will now have a long summer break but his trainer Knight is hoping he will come back better than ever next season.
She said: "Whenever they break a blood vessel it is serious, but it is not career-threatening and hopefully he will come back as good as new next season.
"But it will not have healed in time for the Gold Cup, so it is very disappointing."
