Beatrice Borromeo, 36, is the daughter of Italian aristocrat Don Carlo Ferdinand and married Pierre Casiraghi, the son of Princess Caroline of Hannover, who is the daughter of Grace Kelly.
The long deep red dress is from the Dior Fall-Winter 2021 collection.
She combined it with a gold clutch and matching stilettos.
The royal looked flawless as she styled her hair in a perfect top knot bun.
Husband Pierre Casiraghi was seen wearing a navy blue suit, white shirt and back bow tie.
“What a beauty,” commented a third one.
Beatrice worked as a political journalist before she married Monaco’s Pierre Casiraghi in 2015.
She is always seen wearing impeccable outfits and is now considered one of the best dressed European royals.
When she married Pierre Casiraghi, she wore four different gowns, two by Valentino for her civil service in Monaco and two by Armani Privé for the religious service in Lake Maggiore.