Sass and Bide designers Sarah-Jane Clarke and Heidi Middleton are stepping down from the company they founded 15 years ago to concentrate on "other creative projects."
The brand, which started out in 1999 as a cult denim label sold at London's Portobello Road Market, has since grown into a hugely successful international label, with celebrity devotees including Rihanna, Miranda Kerr and Kate Moss and well received shows at London Fashion Week.
In 2011, department store Myer bought a 65 per cent share of the brand for more than $40m. Sass and Bide will continue as a brand under the direction of Myer, with former Victoria Beckham and Mulberry consultant Anthony Cuthbertson named as the new design director.
"Heidi and Sarah-Jane's departure from Sass & Bide has been in planning for some time as they have been transitioning out of the business," a Myer spokesperson said in a statement to Vogue Australia.
"They go with our great good wishes, and we expect they will be associated with Sass & Bide for a long time."
"When we first decided to launch Sass & Bide, our dream was to build an international brand and to, at some stage, sell the business and explore other creative projects," Heidi Middleton told Vogue.
"At the time we put a 10 year frame on that. We wanted to leave the business in really strong health and leave the brand while it was flourishing. There's a great team in there that we believe can take the business forward."
Middleton is moving to Paris and said she would explore her first love, illustration and art direction.
Clarke said she would remain in Australia with her husband and three children.
The duo have been best friends since meeting at high school in 1992 and said they would always be in touch.
"I'm just excited to have the pure essence of the friendship back, because for a moment there it was just overrun by sales figures and finances," Clarke said.