Elegant Charlene, 35, turned heads in the royal blue velvet dress as she and her husband Prince Albert showed their support for Monaco Against Autism.
The Zimbabwe-born royal, who is the honorary chairman of the charity which was founded last year, accessorised her stunning outfit with navy and silver stilettos, a silver clutch bag and dazzling diamond earrings.
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Adding a colour contrast to her floor-length gown, former Olympic swimmer Charlene wore vibrant red lipstick and styled her hair into a chic quiff.
Prince Albert, 55, chose a smart three-piece tuxedo as well as his black thick rimmed glasses.