The pair were born at Princess Grace Hospital Centre, with Jacques arriving two minutes after his sister Gabriella.
Under the constitution of Monaco, the crown passes according to male-preference cognatic primogeniture meaning that Jacques is his father's heir.
The twins also have two older half-siblings from Prince Albert's previous relationships – Jazmin Grace Grimaldi and Alexandre Grimaldi.
To mark Jacques and Gabriella's ninth birthdays, we take a look back at the House of Grimaldi’s most adorable baby photos - including one of their late grandmother Grace Kelly.
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