Keira Knightley 2007Keira Knightley, 22, is hardly known for her voluptuous behind - until now!

In her latest movie ‘The Duchess’ she parades around with a fake-butt and enough skirts to force the production team to make her trailer larger.

- “Keira has one of the smallest butts in the business and to be able to make her look 1800th century we had to make everything extra large’ a source tells Bang mag.

We think it is going be loads of fun seeing what the wafer thin vixen looks like with some good old booty!