Mr Porter, an online fashion retailer targeted at men, is the latest project for Massenet, 45, founder of Net-a-Porter, a similar service aimed at women. She says Net-a-Porter has more than 3m unique users and is gaining12,000 every month. “They’re brand new customers. That’s up from 8,000 a month last year and 5,000 the year before. So 12,000 people every month wake up and go, ‘I’m going to try shopping online with Net-a-Porter today.’ ” Net-a-Porter was sold in April last year for about £350m to Swiss luxury goods group Richemont, netting Massenet £50m.

A former fashion editor, she kept an 18% stake and reinvested £15m in the business, which made a £23.5m profit on sales of £152.5m in 2009-10. London-based Massenet, who announced recently that she was separating from her husband Arnaud, remains executive chairman.

Natalie Sara Massenet was born in Los Angeles in May 1965, the daughter of Bob Rooney (an American journalist) and Barbara Jones (a model for Chanel). She spent her early childhood in Paris before moving back to Los Angeles in 1976 with her father.In 1997 she met her husband, Arnaud Massenet (an investment banker) at the Notting Hill Carnival. A month later, she moved from LA to be with him.