Charlotte Casiraghi was spotted wearing a ring on her wedding finger at Monaco's Rose Ball, after it was reported by Hola! magazine that the couple were engaged.
The bride-to-be, 31, flashed her engagement ring on the red carpet at the charity event, where Princess Caroline of Hanover arrived with designer Karl Largerfeld.
The news comes just one week after the brde's step brother, Prince Christian of Hanover, tied the knot with his fiancée Alessandra de Osma in a lavish celebration attended by model Kate Moss in Peru.
Prince Christian and fashion designer Alessandra exchanged vows in the bride's native Lima, and European royalty and their celebrity friends descended on the city for an event to remember.
The guestlist was a veritable who's who of European monarchy, including Britain's Princesses Beatrice and British royal bride-to-be Eugenie, Monaco's Beatrice Borromeo and Pierre Casiraghi, Greece's Princess Olympia with her father Crown Prince Pavlos and legendary supermodel Kate Moss with her boyfriend Count Nikolai Von Bismarck.
Magazine Hola! had reported that Charlotte and Dimitri were engaged some weeks ago, however according to Hello! this is the first time the couple have confirmed the news.
Hola! reports that the couple are set to marry this summer in Sicily, where the groom's mother has a private villa.