Sienna Miller thinks Keira Knightley is a ''timeless movie-star''.

The 31-year-old actress, who starred alongside Keira in 2008 film 'The Edge Of Love', thinks her close friend has a unique style and can pull of any outfit because of her classic appearance.

She said: ''The first thing that springs to mind [when thinking about Keira] is the 1940s. I think of her as glamorous in that kind of timeless movie-star way, but she can be grungy in this very cool 90s way.

''You say this about people who have style, but it's true - she genuinely doesn't think about the way she looks or how she puts herself together. She could throw on a bin bag and look beautiful.''

Keira, 28, has been the face of numerous beauty and fashion campaigns - including Chanel's Coco Mademoiselle perfume - and the brunette beauty enjoys exploring different looks to create distinctive feels for the brands.

She told Marie Claire magazine: ''I like the fantasy of fashion, creating a different person and dressing up like her. Putting on a flowery dress when it's raining brightens up the world.''