The 31-year-old actress, who starred alongside Knightley in 2008 film "The Edge Of Love", said her close friend has a unique style and can pull of any outfit because of her classic appearance, reported Contactmusic.
"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," Miller said.
"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," she had said.