The 24-year-old actress was spotted in an oversize Elvis Costello-style pair of spectacles after leaving rehearsals for her new play in London.
She teamed her heavy black-rimmed glasses with a black leather jacket, jeans and men's brogues.
Her hair, usually sleek and glossy, was loose and wavy.
The girl who has redefined red carpet glamour with a wardrobe of elegant gowns was very much off duty.

We knew this would happen sooner or later. It looks like the remake of the 1964 George Cukor classic, My Fair Lady has gained momentum. Keira Knightley was rumored to star as the lead character in the new version of the film forever, and according to The Telegraph, she has officially won the role of Eliza Doolittle and beat out Scarlett Johannson to do it.

A play starring Keira Knightley has taken £1million at the box office in just four days - even though it hasn't opened yet.
The phenomenal advance sales have caused a stir in theatreland, as it's normally just musicals that bring in the mega bucks.
The Misanthrope marks Keira's West End stage debut and the news of her casting was only announced a week ago.

Keira Knightley has been tipped to star in a new version of 'My Fair Lady'.
The 'Pirates of the Caribbean' actress is reportedly in negotiations to play Eliza Doolittle in Emma Thompson's adaptation of the classic rags-to-riches tale.
Anne Hathaway and Scarlett Johansson are also being considered for the role, which was originally played by Audrey Hepburn.
An insider said: "Keira and Scarlett are the only two real contenders and Keira's the favourite. She's the most natural Eliza people have seen.
"She has worked on her singing voice for a year and will get better and better."
The film's director Danny Boyle – who won an Academy Award for 'Slumdog Millionaire' earlier this year – is also believed to want Knightley to get the part.
The 24-year-old actress is said to be "scared" about taking on such an iconic role, but excited about the challenge it would present.
Filming is expected to start late next year.

Hathaway, 26, the only actress under 30 to receive an Oscar nomination in the last twelve months, tops the poll by lovefilm.com.
Knightley, who has appeared in Pirates of the Caribbean and The Duchess, topped the poll last year but could only manage second place this time round.
Compilers of the list studied the commercial and critical success of actresses under 30 in the previous 12 months.
In third place came Hathaway's Brokeback Mountain co-star Michelle Williams after indie film appearances in Synecdoche New York and Wendy and Lucy, whilst another Devil Wears Prada graduate, the British actress Emily Blunt, came fourth after roles including the lead in Young Victoria.