More than a dozen of the Queen's horses are being sold off by the King - including her final Royal Ascot winner.
The monarch inherited his mother's Sandringham stud which was established in 1886 by Edward the Prince of Wales and has produced a series of high-profile winners.
Auction house Tattersalls, in Newmarket, said there had been significant interest in the sale, which is the first time horses from the Royal Stud have been sold since the Queen died in September.
But marketing director Jimmy George said it was a relatively frequent event.
"Most significant owner-breeders sell a proportion of their stock every year because all owner-breeders are constantly breeding young stock," he said.
"I've worked here an awfully long time, since 1986, and every single year we would have horses to sell on behalf of the Queen, in the past, and now on behalf of the King."
Among those being sold during the four-day sale are Just Fine, the first of the King's winners after he inherited the stud, which sold for 300,000 guineas on Tuesday.
Love Affairs, which won at Goodwood just two days before the Queen died, and Tactical, the late monarch's final winner at Royal Ascot in June 2020, will be sold on Wednesday.
The horses were signed up for the sale days before the Queen died in last month.
A key patron of the racing industry, she was actively involved in the breeding of the Royal Stud on her Sandringham Estate.
Although there has been speculation that King Charles may not be as invested in the sport as his mother was, experts say the sale of horses are not necessarily a sign the collection is being reduced.
Mr George said, regardless of who was selling the animals, breeders were only interested in potential winners.
"As a rule, the breeders here are not really diverted by who owns the horses," he said. "It's what the horses have achieved and what they believe they can go on to achieve that's they key to how much attention they will receive."
The Tattersalls Autumn Horses in Training sale continues until Thursday.
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