The RSPCA has lost out on part of a£400,000 legacy after a pet dog was put down.
Blackie's owner Claude Atack, 80, from Caernarfon, Gwynedd, had specified that any charity which found his pet a home would get a large part of his estate.
Solicitor Dewi Pritchard Jones thought the dog was in good health and was shocked he had been put down.
But the RSPCA said Blackie was found to suffer from numerous health problems, and was put down on humane grounds.
Mr Atack was found collapsed at his home by concerned neighbours when they realised they had not seen him walking sheepdog Blackie on 29 January.
"He walked Blackie four times a day, and he lived for the dog," said Mr Pritchard Jones.
Mr Atack died in hospital on 1 February.
A neighbour initially looked after Blackie, then he was handed over to the RSPCA.
"I wasn't concerned because their leaflets state that they do not put animals down without good reason. I thought he was safe," said the solicitor.
He added that Mr Atack had stated in his will that his estate should be shared between different charities, but with no less than one fifth going to an animal charity.
I am angry about what happened
But verbally he had told his solicitor that more of his estate should be given to any charity which found Blackie a new home.
He had stipulated that he could be "especially generous" to any charity which found his dog a home.
Mr Pritchard Jones said that a couple, who do not wish to be named but who knew Mr Atack, came forward to offer Blackie a home on 8 February.
They traced him to an RSPCA kennel at Shrewsbury, but were told he had already been put down on the day he was handed in.
"The old gentleman thought the world of him and at any sign of illness he would be whipped off to the vet," he said.
The vet said he (Blackie) had cataracts and was overweight, as a dog which is pampered tends to be," he added.
The incident would have broken Mr Atack's heart, he said.
"He lived by himself, it was just him and the dog," he added.
The solicitor added that the money - in excess of £400,000 - would be shared between other charities.
"I am angry about what happened, because I have a dog which is 15 years old, and you can't put them down just because they are old," he said.
"I think Blackie would have made someone elderly a lovely companion, as he was used to being around an older person, and they often don't want the hassle of getting a puppy," he added. RSPCA officials told Mr Jones Blackie was put down because of his age and poor health. But this is disputed by the solicitor.
Mr Jones added: "The dog was 10 years old but definitely not in poor health, as Mr Atack would regularly take the dog to a vet and would spare no expense over its health. The vet confirmed that apart from his age the only thing wrong with the dog was the early stages of cataracts and that it was slightly overweight."
Mr Atack, who was born in Salford, moved to North Wales more than 20 years ago to oversee the family steel fabrication business. He lived alone and had no close family.
The RSPCA said they were aware of the case, but no one was available to comment last night.