Prince Jacques and Princess Gabriella attended the International Circus Festival on Sunday. The eight-year-old siblings, who donned matching scarves, were greeted by performers on the red carpet.
However, mother Princess Charlene, who turns 45 tomorrow, did not attend the show.
Albert’s sister Princess Stephanie, 57, was also present alongside her 30-year-old son Louis and 24-year-old daughter Camille.
Louis walked arm-in-arm with his wife Marie Chevallier, also 30, who is expecting the couple’s first child.
The British monarch and Monégasques Prince have a friendly relationship.
Albert described Charles as “a most patient man”.
He added: “A very educated man and someone with a great sense of humour.”