Asos has acquired Topshop and other Arcadia brands in "a hugely exciting moment" as it seeks to "drive growth globally and accelerate its brand strategy".
In a busy week for Britain's online retailers, Asos Plc, Boohoo's bigger rival, is already in exclusive negotiations with Arcadia to buy Topshop, Topman, Miss Selfridge and HIIT brands.
Although the deal includes the brand and stock, it does not include the shops, placing the affected brands' physical stores including the Topman and Topshop store in the Eastgate Centre, at risk of closure.
The transaction is expected to complete on February 4.
A spokesman for administrators Deloitte said it included £265m for the brands, £30m for stock and £35m for stock on order.
Elsewhere, Boohoo recently bought the Debenhams website for £55 million after the company was forced to shut its doors past year.
The process to secure new owners for Burton, Dorothy Perkins and Wallis remains ongoing via exclusive discussions with a potential purchaser.
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Evans, another retailer within the Arcade portfolio was sold to Australia's City Chic for £23m in December.
All were previously part of Sir Philip Green's once all-mighty Arcadia Group. This means hundreds of outlets will close and the position of thousands of employees are at risk in an industry that already shed more than 100,000 jobs previous year.
"These are strong brands that resonate well with our core customer base".
The four brands acquired in Monday's deal posted sales of £1 billion ($1.8 billion), ASOS said.
"We have been central to driving their recent growth online and, under our ownership, we will develop them further, using our design, marketing, technology and logistics expertise, and working closely with key strategic retail partners in the United Kingdom and around the world".
Some 15,000 retailing jobs in Britain are in peril after Arcadia Group, owner of some of the country's best-known fashion chains like Topshop, confirmed they have been acquired by ASOS.
But all existing stores - including a number across Kent - will close.
