Jessica Harrington led the tributes to Alan Potts after the leading National Hunt owner died at the age of 80.
Potts was one of the powerhouse names in jumps racing and was responsible for Sizing John, who won the Cheltenham Gold Cup in March.
Potts' wife, Ann, also died in August after a long illness.
Harrington, who trains Sizing John and the bulk of the Potts horses in Ireland, told Press Association Sport: "It's a big shock. It wasn't something we were expecting. I found out through an email from his company this morning.
"He was a certain age but he'd just been away on holiday to Mauritius and Africa and come back. I'd talked to him a couple of times and he seemed to be in great form.
"For him to die so soon after his wife - it's sad.
"I've only trained for him for just over a year but we've been incredibly lucky together. It was a fantastic year."
Alan and Ann Potts enjoyed an incredible 2016-17 campaign as the Harrington-trained Supasundae won the Coral Cup at the Cheltenham Festival, while Fox Norton, Sizing Codelco and Pingshou were all scorers at the Grand National meeting at Aintree in April.
The couple first came to prominence within National Hunt racing after their distinctive yellow and green silks were worn by the Henry de Bromhead-trained Sizing Europe, who claimed eight Grade One triumphs in a magnificent career.
Robbie Power, who was the retained rider for Potts in Ireland and also rode Sizing John in the Gold Cup, said: "It's awful news - very sad - and so soon after his wife, too."
In 2016 the Potts family removed all of their horses from De Bromhead's yard, sending many of them to several trainers across Ireland.
Dorset trainer Colin Tizzard also inherited a sizeable string, with a number of the Potts horses in line to run at the big three-day meeting at Cheltenham this weekend.
Tizzard told Press Association Sport: "It came as quite a surprise as I was only talking to him a few days ago.
"He was a self-made man. He could be quite demanding but he could be absolutely brilliant company - that was the sort of person he was.
"He made a lot of money from scratch and he definitely brought our stable a few gears forward and he will be sadly missed.
"We've had some brilliant days and we had a brilliant meeting at Aintree and then went over to Punchestown.
"Ann was still around then and Ann and Alan together were lovely company. Ann was a lovely lady and we all had some brilliant times together.
"I think going over to Punchestown and winning the Champion Chase with Fox Norton was brilliant along with Sizing Granite and Sizing Codelco winning there.
"Going to Ireland and beating the Irish there was special. We sat with him for dinner for three or four days there and spent a lot of very happy times together.
"I am not quite sure (what will happen) about the horses. They have been sorting out this huge business of his for a few years. I think it will be sorted soon and we will then find out what will happen."
Tom O'Brien rode the Potts-owned, and Tizzard-trained, Finian's Oscar to victory in the Tolworth Hurdle at Sandown in January.
He said: "My condolences to all his family. I am very grateful to have ridden for him and to have ridden a Grade One winner in his colours.
"It is a very sad day and I'm thinking of his family. I only met Alan a few times at Cheltenham. Unfortunately I didn't get to know him well. He loved his National Hunt racing. He was a competitive man and always wanted to be the best."
Jim Dreaper used to train horses for Ann and Alan Potts in Ireland, and told Press Association Sport: "It's a sad day. I had horses for him for 10 to 12 years now. He was a great sportsman and a gentleman.
"He loved to win, like us all, but he took the ups and downs of it well. It's a sad loss, especially so soon after losing his wife.
"It was just marvellous for him that they had their day at Cheltenham in the Gold Cup last year."