The pair, who met at school in the early 1990s and started out selling jeans and denim wear at London's Portobello Street market, have relinquished their stake in the brand, which raked in more than $50 million in global sales, to Myer.

The retailer bought a 65 per cent stake in the business in 2011 for $42.5 million before snapping up the remaining 35 per cent in October last year. At the time, Clarke and Middleton maintained their executive roles and chairs on an advisory board for the brand. Up until two weeks ago, the pair were the public face of the label, which now includes ready-to-wear, accessories and special diffusion lines that raise money for the Make-A-Wish Foundation and the United Nations.

''Both Heidi and Sarah-Jane have been slowly transitioning out of the business, and it has now reached a point where both girls feel confident that the business will go on to grow and thrive without their day-to-day involvement,'' a spokeswoman for the pair told Fairfax Media.

''The girls leave behind a rich legacy of creating a brand that is built on spirit and heart, qualities that are deeply etched in the collections, the communications and its people. Those qualities will continue to define and drive the brand for years to come.''

Middleton, a former graphic artist and breast cancer survivor from Brisbane, has relocated to Paris with her family and plans to work on a ''personal creative project''. She hopes to open an exhibition there within the next year.

Clarke, the ''sass'' to Middleton's ''bide'', is more philosophical of the next chapter, telling Vogue: ''I'm just excited to be walking into the unknown and I'm enjoying this freedom. I feel quite calm about the future so it's quite open to the universe right now.''

Myer confirmed Middleton and Clarke were involved with the recruitment of a new design and creative team to be headed by Anthony Cuthbertson and Bonnie O'Hare.

''Myer has worked closely with Sarah-Jane and Heidi to establish a strong team of designers ... Myer wishes Heidi and Sarah-Jane well, they go with our great good wishes, and we expect they will be associated with sass & bide for a long time,'' a spokeswoman said in a written statement.

New design director, Cuthbertson, is the creative director of Australian label David Lawrence and has previously consulted to high-end fashion houses including Victoria Beckham, Mulberry and Scanlan & Theodore. He was responsible for David Lawrence's push into the luxury market last year with the 80-piece DL Atelier collection.

However, one gripe the designer has with the Australian fashion landscape is the lack of menswear options, perhaps something he may pursue with his new venture with Myer.

''I only shop overseas as I find it hard to buy great menswear here,'' he told The Australian Financial Review in January.

Cuthbertson has been joined by art director Bonnie O'Hare, a creative all-rounder and graphic designer who has worked for Tommy Hilfiger, Hugo Boss, Calibre and youth brand Bardot.

It is understood Myer now plans to expand the sass & bide brand into emerging areas of fashion retail such as lingerie.