The founder of upmarket fashion website Net-A-Porter is set for a reported £70 million payout after the firm she launched 15 years ago announced a merger with an Italian rival.

Former fashion journalist Natalie Massenet, who founded the business from her London flat in 2000, will see Net-A-Porter merge with Italy's YOOX to create an enlarged firm with annual sales of €1.3 billion (£944m) and adjusted earnings of €108m (£78m).

Ms Massenet will be executive chairman of the combined group, which will cover 180 countries and last year took 5.8 million orders for such designers as Alexander McQueen, Jimmy Choo and Dolce & Gabbana.

Californian-born Ms Massenet sold a controlling stake in Net-A-Porter to Richemont in 2010 for £50 million.

The Swiss luxury goods firm, which also owns Dunhill, Cartier and Montblanc, will own 50 per cent of the combined firm, with the current shareholders of YOOX owning the remainder.

Ms Massenet said: "Today, we open the doors to the world's biggest luxury fashion store."

Richemont chairman Johann Rupert said: "The merger of the two leaders will further enhance an independent, neutral platform for a sophisticated clientele looking for luxury brands."

Net-A-Porter employs more than 2,500 staff in London, New York, Hong Kong and Shanghai.

The new YOOX Net-A-Porter group said the merger will combine two market leaders with a customer base that comprises more than two million "high-spenders" and 24 million monthly unique visitors.

It said the deal is expected to close in the first half of September, adding that the combination would achieve annual savings of €60m (£44m) by the third year following the completion of the merger.

The group said it plans to raise €200m (£145m from investors following the combination to fund further growth.