Jane Shepherdson has left Whistles eight years after becoming co-owner of the fashion label which she has re-invented.

The former Topshop boss nurtured Whistles into one of the high street’s most well-regarded brands, helping to earn her a CBE for services to UK retail business in 2014.

Shepherdson’s departure comes less than six months after Whistles was bought out by South Africa’s Foschini Group. At the time of the takeover, Shepherdson retained her 20% stake and said she was committed to remaining at the company.

The brand’s fans include the Duchess of Cambridge and Samantha Cameron and its clothes are stocked by Bloomingdale’s in the US and Harrods in the UK. Foschini said it wanted to expand the company, which added a menswear range in 2014, into new markets.

But on Tuesday, Whistles confirmed that Shepherdson, who has already signed off the brand’s spring/summer and autumn/winter 2017 collections, had stepped down. A spokesperson told Vogue she had left to “work on her charity projects and is planning to travel, initially spending time on the west coast of America”.

Sherpherdson will hand over to brand director Helen Williamson, managing director Justin Hampshire, and creative director Nick Passmore.

One source said Shepherdson had disagreed with the new owners over the running of the business and its attempts to introduce processes used at some of the other brands it owns, such as Phase Eight.

Whistles said after experiencing challenging trading conditions last year, the company had returned to profitability in 2016 as customers responded well to its spring and summer collections.

Jane Shepherdson said: “I am really proud of what we have achieved at Whistles.”

Ben Barnett, chairman of Whistles, added: “We would like to thank Jane for her outstanding contribution to the rebuilding of the Whistles brand. She has established a clear direction for the future development of the brand and in Helen, Justin and Nick we are privileged to have an exceptional management team to realise this vision.”

The loss of Shepherdson is likely to be a blow for Whistles. She became one of the most influential people in British fashion during her time at Topshop.

Having worked her way up from the shop floor, Shepherdson took over as brand director of Topshop in 1999. Within six years, profits had gone from £9m to £110m, and had become a retail sensation. It is now the cornerstone of former BHS owner Sir Philip Green’s empire with stores around the world.

Founded in 1976 by husband and wife team Richard and Lucille Lewin, Whistles has endured fluctuating fortunes over the years.

Shepherdson’s buyout was backed by the former Icelandic retail investment group Baugur, which collapsed in 2009. The group later refinanced with some loans from the then nationalised Glitnir bank.