He's staying with the business as a non-executive director, though the change at the top unsettles investors nonetheless, sending the shares 2.6% lower to £29.06.
Charismatic Robertson (pictured above) built ASOS from an online minnow with the moniker 'As Seen On Screen' – it originally sold clothes and accessories seen on film or TV or worn by celebrities – into a world class online retailer and stock market darling trading on a stratospheric multiple of earnings.
Under his stewardship, the pure-play online retailer built a dominant position in the 20-something fashion niche and burgeoned into an AIM giant generating rapid-paced global growth.
Yet the 'fast fashion' purveyor was brought back to earth by a torrid 2014 marred by profit warnings, slowing international sales amid stiff currency headwinds and also a fire at its Barnsley warehouse.
Sentiment toward the stock was hardly helped by Robertson's sale (28 Jan) of £20.2 million worth of shares at the start of 2015, a disposal thought to be for tax purposes, although recent market missives have soothed sentiment.
April saw ASOS post in-line interim results and issue a positive second half outlook, while a strong third quarter update in July continued the confidence rebuilding exercise, with the retailer demonstrating sustained sales momentum and achieving better-than-expected gross margins for the four months to June.
Well-qualified chief operating officer (COO) Nick Beighton (pictured below), who originally joined ASOS in April 2009 as numbers man, succeeds Robertson in the CEO hot seat with immediate effect.
Chairman Brian McBride says 'we are fortunate to have such an able successor for the CEO role in Nick Beighton. Nick has unique experience of the company built over six years, equipping him to drive ASOS along its growth trajectory to become the world's leading online fashion retailer for 20-somethings'.