Prince Albert's older sister Caroline was the epitome of regal elegance when she wore a sapphire velvet gown very similar to one worn by Charlene last week.
While Charlene's form-fitting gown was sleeveless, 56-year-old Caroline opted for long sleeves and a looser fit.
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Despite striking similarities between their dresses, the two Monegasque royals showed off their individuality with their choice of accessories.
Grace Kelly's eldest daughter Caroline chose a matching pale blue necklace and a pair of earrings while Charlene, 35, opted for dazzling diamond statement earrings.
For Tuesday's festivities in Monte Carlo, Charlene chose a sophisticated full-length black ensemble.
Earlier in the day former Olympic swimmer Charlene and her husband Albert attended a mass at the cathedral to mark the day.
Princess Caroline's younger sister Princess Stephanie attended other ceremonies earlier in the day.
Charlene and Albert were also seen waving from the Palace balcony during a parade for the celebrations.
The royal couple, who tied the knot in 2011, had been busy supporting the Red Cross earlier in the day, visiting a gift-giving event for the elderly at their headquarters.