The 27-year-old sported a grey, floor-length gown that accentuated her growing bump and she joined her brother Andrea Casiraghi and their mother Prince Caroline at the dinner.
The Monégasque royal party was completed by Princess Stephanie, Caroline's sister, who joined the trio at Monacos' luxurious Hotel Hermitage to support the charity their mother Princess Grace founded 50 years ago.
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Princess Grace of Monaco founded the Amade Mondiale Association, of which Caroline is now president, in 1966 with the aim that it would help support needy children around the world.
Caroline's radiant daughter is now in the third trimester of her pregnancy and her baby, whose father is Charlotte's actor boyfriend Gad Elmaleh, is due at the end of the year.
Gad recently spoke out denying rumours that he was engaged to Prince Albert II's niece in an interview with the Washington Post.
"No, I'm not engaged," said the 42-year-old comedian, who was setting the record straight after Charlotte was seen wearing a large ring.
During her pregnancy Charlotte has been spotted shopping for baby clothes in Italy, Monaco and Paris and has also been undertaking many official duties including her beloved riding events.