Trained by Paul Nicholls and owned by Andy Stewart, the 11-year-old was denied an almost-certain fifth stayers’ crown last season through injury, having to miss Cheltenham.
He returned after 420 days off the track to be third in the Cleeve Hurdle at January, and had been expected to improve markedly on that effort.
But it was not to be as youngsters More Of That and Annie Power fought out the finish to the three-mile championship.
Nicholls immediately announced his racing career was over.
Big Buck’s was taken straight to the stables following the race, but after his retirement was confirmed, the ever-popular runner returned to the paddock to say farewell with one last walk around the ring.
Nicholls said: “He’s going to have an honourable retirement, it’s a sad day but it’s good to end in one piece.
“Andy and I have been talking about it and I couldn’t improve him any more on what he’s done today. We won’t ask him to run again as he’s been a wonderful horse and wonderful for racing.”
Nicholls went on: “Younger legs beat him today. I could see halfway round we were in a bit of trouble and retirement is the right thing to do.
“He wasn’t jumping quite as fluently and his legs aren’t quite what they were.
“He’s been a legend. You can see how hard it is to win four World Hurdles, let alone trying to win five when they are a bit older and have had some problems.
“We gave it a go. That’s what we wanted to do, but you have to be sensible and draw stumps at the right time and now is that time.
“He’ll have a lovely home now and be well looked after.
“To run him again would be madness and it’s not that emotional (to retire him).
“I’m delighted, to be honest. I would hate to see him run round getting beaten and for anything to happen to him.
“It’s been awesome.”
Stewart said: “The great horse is not as great as he was when a nine-year-old.
“He had 420 days off (before returning in the Cleeve Hurdle) and he’s obviously not sparkling any more. At Fishers Cross beat him in the Cleeve and has done so again and I think he is finding the years getting to him.
“We have done as much as we possibly can and there’s no way we can improve on that – what you saw today is as good as he is but he owes us nothing.
“He’s going back to Ditcheat where all my other retired horses are, and he’ll be with Cenkos.
“It’s been very flattering the way the public have taken to him.
“He’s probably one of the greatest, if not the greatest, staying hurdler of all-time, and it’s time to enjoy his retirement.
“He’s been great for the public, great for racing and I love him to death.
“He won 18 out of 18, he’s won 18 out of 20 now including his four World Hurdles.
“I’m going to enjoy feeding him and giving him his Polos while he’s not under any pressure.
“This is the best racecourse in the world and this is the best meeting in the world – the Olympics of National Hunt racing.
“To retire him now is absolutely correct. He still wants to do it, but he can do it at Ditcheat and in the privacy of Paul Barber’s empire.”
Big Buck’s reverted to hurdling after unseating Sam Thomas in the 2008 Hennessy Gold Cup, and went on to enjoy an 18-race winning streak before being beaten in the Cleeve, enjoying a fantastic association with Ruby Walsh along the way.
He won the World Hurdle for four consecutive years from 2009 to 2012, and won well over £1,250,000 in career earnings.
Sam Twiston-Davies, who rode Big Buck’s on his final two starts, said: “He’s an amazing horse and it is a dream for me to have ridden him. As far as the race was concerned everything went as I would have liked, I was in the right place at the right time but obviously he is 11 now.
“Just when we turned in, he didn’t have the legs.
“We hadn’t gone mad early and we picked up nicely but there were young legs against us.
“Mr Nicholls was happy when we came back – as happy as you can be with an 11-year-old coming back after a long absence. He is back safely and in one piece and that is the main thing.
“I am as happy as I have ever been finishing fifth.”