Knightley, who has become a major film star, has mixed feelings about the culture of celebrity and being famous - which another high-profile role is likely to increase.
"Once you become famous you get completely dehumanised. I think people forget there is a person in there trying to deal with it," she says.
"Partly the way you deal with it is by not reading, not looking and seeing any of it and burying your head in the sand. It is the only path to sanity," adds Knightley.