Kate Middleton looks the part of a princess in recycled dress, Queen's jewels

Kate Middleton looked the part of a princess as she attended a gala Tuesday night at the National Portrait Gallery.

Perhaps the most impressive part of all, however, was the fact that the Duchess of Cambridge wore a dress she debuted back in October at a Kensington Palace dinner.

The $3,300 dress comes from Jenny Packham's Autumn/Winter collection, and features chiffon off-the-shoulder sleeves, a heart-shaped neckline, and a black velvet belt designed to highlight the new mom's tiny waist.

Only this time, Middleton added a feature only the daughter-in-law of the Queen of England could: a diamond-encrusted necklace originally crafted in the 1930s by Cartier. Given to Queen Elizabeth II as a wedding present from the Nizam of Hyderabad, it boasts a chain of 38 diamonds and a pave-set center.

The gala represented a 100 Women in Hedge Funds dinner designed to raise money for the charity Action on Addiction.

Middleton recently returned from a trip to the Caribbean, where she met up with her family in celebration of her mother's 59th birthday. The Middletons stayed on the island of Mustique, where they visit every year.

Although the duchess brought 6-month-old George with her, William was forced to stay at home in order to stay on top of his studies.

Purchased more than 50 years ago by the Scottish noble Colin Tennant, Mustique remains a star-studded vacation spot to this day, with Paul McCartney, Mick Jagger and Jeremy Clarkson just among those with a place there.