Monaco's Charlotte Casiraghi believes the key to a success relationship is a shared "passion for the truth."

Charlotte Casiraghi and Gad Elmaleh

Charlotte Casiraghi and Gad Elmaleh

The 29-year-old royal has been dating her beau Gad Elmaleh, with whom she has 21-month-old son Raphael, for over three years and is confident they're a strong partnership because they share similar beliefs on life.

The stunner - who is eighth-in-line to the throne - told France's Philosophie magazine: "I believe that the key to a long and happy relationship is when you both share a passion for the truth, for life."

Charlotte - whose grandmother is the late Princess Grace Kelly - met Gad, 44, at a party in 2011 and had sought to keep their relationship as private as possible ever since.

The couple made their first public appearance in 2013 at the Bal de la Rose and are thought to have split their time between living in France and Los Angeles, California.

Meanwhile, Charlotte's comment on relationships comes four months after rumours began to surface she and Gad had ended their romance due to their busy schedules.

A source said at the time: "It's sad. Mostly, this is a couple that drifted apart over their careers. He wasn't around enough - and she wanted a father for her son."

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