Britain's Duchess Catherine opted for a Topshop dress for the Harry Potter tour today (26.04.13).

The 31-year-old royal - who is expecting her first child with Prince William in July - indulged her love of high-street designers by wearing the £38 polka dot piece as she joined her husband Prince William and brother-in-law Price Harry for the tour around Warner Bros. Studios is Leavesden, Hertfordshire, East England.

Catherine - known as Kate Middleton prior to her nuptials in 2011 - teamed the affordable dress with black suede shoes and a matching Ralph Lauren jacket pushed up at the sleeves.

The brunette beauty is no stranger to the popular store after being spotted browsing the maternity section of London's Oxford Street store earlier this year.

An excited onlooker, username KtSu, wrote on Twitter at the time: ''Oh Just an average day, Kate Middleton smiled at me! :) oh best bit... This was in Topshop! Truly Beautiful :) (sic).''

The royal trio were treated to a look behind-the-scenes of the wizarding franchise earlier today, where they learned how to use magic wands and walked down the winding streets of the film's iconic Diagon Alley.

While onlookers were in awe of Catherine's casual and stylish ensemble, her husband was especially impressed with props from Batman flick 'The Dark Knight Rises'.