The 24-year-old twin sisters have opened up about their billion dollar empire that includes three fashion lines - The Row, Elizabeth & James and Olsenboye - in the latest issue of Vogue magazine.

The pair, who are known for their kooky style, pose in polka-dot Tom Ford pyjamas in the accompanying photo shoot.

In the kooky shot, they are pictured balancing on stilts on the beach while clutching empty wine glasses. 

'We think big... huge!': Mary-Kate and Ashley Olsen pose in pyjamas as they reveal secrets behind their billion dollar empire - Ashley Olsen - Mary-Kate Olsen

The blonde-haired sisters also posed for famed photographer Bruce Weber in dusty pink dresses from from their own range while they peeped over an antique Brigitte Bardot book.

The sisters insist that unlike some celebrity brands, they are heavily involved in every aspect of the design process.

The pair were were initially met with cynicism when the started out in the fashion world.

'We hired a showroom and talked buyers through,' Ashley says.

'People would drill us about fabric, where we'd make it,' Mary-Kate adds. 'The first season, customers bought it, so the stores came back. And drilled us again.'