The crowds had been gathering for days, and the red carpet was ready and waiting for the cast of Harry Potter to premiere their final film. And fans certainly were not left disappointed when Emma Watson arrived in Trafalgar Square looking simply magical. The 21-year-old actress brought the glamour in a floor-length tiered Oscar De La Renta ruffled gown, a dress that made her look like a fairytale princess. Scroll down for video Fairytale princess: Emma Watson looked stunning in her Oscar De La Renta gown as she took to the red carpet Leading lady: Emma Watson played to the crowd as she posed for pictures on the red carpet in Trafalgar Square The dress was teamed with equally exquisite Boodles' 'Cabaret' white gold earrings with citrine briolette drops worth £7,680 and a matching ring worth £10,670 But her smiles didn't last long as Emma and many of her co-stars broke down while paying tribute to the final film in the franchise, Harry Potter And