Knightley was cast in the role because of her close resemblance to Portman; even the two actors' mothers had difficulty telling their daughters apart when they were in full make-up.
Knightley blev valgt til rollen grundet hendes store lighed med Portman; selv de to skuespillerers mødre havde svært ved at skelne døtrene fra hinanden, når de var iført fuld make-up.