The Atonement actress was required to master some complicated choreography while filming the drama, based on Russian author Leo Tolstoy's 1870s classic, but she soon realised she was among the worst dancers at the shoot.
Knightley tells U.K. morning show Daybreak, "I found out that I'm not a very good dancer. We spent about a month trying to work on it. But I did find out that Aaron Taylor-Johnson is a completely brilliant dancer and upstages absolutely everybody, which I was really annoyed about."
