Keira Knightley played Amidala's most trusted handmaiden in Star Wars: The Phantom Menace.
There can be no doub that Knightley was casted for that part mostly because of her resemblance to Natalie Portman (in the movie it is also pointed out that Amidala's handmaiden are partly choosen because of that).
So yes, Natalie Portman and Keira Knightley look like each other.