Business in the south east appointed with a Royal Warrant by Queen Elizabeth II must now reapply for the honour under the new King.
The late Queen's official glove maker, clock supplier and repairer, and her piano restorer are among them.
The warrant symbol shows that companies meet exacting standards, and regularly supply the Royal Household.
Cornelia James has made the Queen's gloves since 1946, and her daughter Genevieve said it had been an "honour".
Whilst still a princess, Queen Elizabeth II first turned to the company near Lewes, East Sussex, for her gloves.
Cornelia James was later commissioned to create a suitcase full of gloves for the Queen's honeymoon.
The family firm has made bespoke garments for all of the Queen's official engagements since, and was granted the warrant in 1979.
Genevieve James, now the creative director of the firm named after her mother, said: "It's been wonderful, and it's an honour.
"It's a mark that you are the best at what you do, and that makes us very proud."
She said she was "star-struck" when she met the Queen and her death had "hit quite hard".
"It seems like there's a piece of me that's gone and I feel quite emotional about it," she added.
Dave Winston, who founded The Period Piano Company in Biddenden, Kent, regularly maintains Queen Victoria's piano.
He said: "It is played now and again. It was used for a Prom a few years ago and moved to the Albert Hall, which was pretty amazing.
"King Charles is very interested in supporting the arts and small niche businesses so I think he'll really encourage people like me, which is great."
For clocks the Queen turned to H S Walsh & Sons, in Biggin Hill.
CEO Patrick Sheehan said he was saddened by the news of the Queen's death.
He added that having a warrant was "a lovely club to be in" and found people had more trust in the company as a result.
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