Sienna Miller: Twenty8Twelve at London Fashion Week!

Sienna Miller and big sis Savannah Miller pose backstage at their Twenty8Twelve fashion show during London Fashion Week Spring/Summer 2010 at London’s May Fair Hotel on Monday (September 21).

“Usually I get my best ideas in the middle of the night,” Sienna told People. “We text all the time and we’re always on BBM (BlackBerry Mobile Instant Messaging),” added Savannah.

Sienna is currently starring in the Broadway play After Miss Julie with fellow Brit Jonny Lee Miller.

10+ pictures inside of Sienna and Savannah showing Twenty8Twelve at London Fashion Week…