Celebrity sisters Sienna and Savannah Miller pose for their portrait at the launch of their fashion label's latest collection: Twenty8Twelve. London F Stock Photo - Alamy

Actress Sienna Miller and fashion designer Matthew Williamson arrive at Somerset House for the opening night of a Matthew Williamson exhibition celebrating the October launch of a book dedicated to the of

Sienna Miller at London Fashion Week, London, England, UK Stock Photo - Alamy

Sienna Miller London Fashion Week Spring/Summer 2012 - Burberry Prorsum - Arrivals London, England - 19.09.11 Stock Photo - Alamy

Celebrity sisters Sienna and Savannah Miller pose for their portrait at the launch of their fashion label's latest collection: Twenty8Twelve. London F Stock Photo - Alamy

Savannah miller hi-res stock photography and images - Alamy

Savannah miller and sienna miller hi-res stock photography and images - Alamy

Savannah miller hi-res stock photography and images - Alamy

Celebrity sisters Sienna and Savannah Miller pose for their portrait at the launch of their fashion label's latest collection: Twenty8Twelve. London F Stock Photo - Alamy

British actress Sienna Miller and designer Savannah Miller attend their Twenty8Twelve's Autumn/Winter collection catwalk show at London Fashion Week in London on February 22, 2009. (UPI Photo/Rune Hellestad Stock Photo - Alamy

Actress Sienna Miller and fashion designer Matthew Williamson arrive at Somerset House for the opening night of a Matthew Williamson exhibition celebrating the October launch of a book dedicated to the of

Savannah miller hi-res stock photography and images - Alamy

Sienna Miller and Savannah Miller London Fashion Week Spring/Summer 2011 - Twenty8twelve Fashion Show-Backstage The Old Sorting Office London, England - 18.09.10 Stock Photo - Alamy

2,191 Savannah Miller Photos & High Res Pictures - Getty Images

Sienna Miller London Fashion Week Spring/Summer 2012 - Burberry Prorsum - Arrivals London, England - 19.09.11 Stock Photo - Alamy