Princess Charlene's meeting with Pope Francis has left fans of royal fashion wondering why she broke with tradition.

The wife of Prince Albert II was dressed in the traditional black dress and veil that a woman would wear to meet the head of the Catholic Church - but Charlene actually has a special privilege given to only seven women in the world.

Called a

privilège du blanc

, the Monagues royal is one of the few people allowed to wear a white dress and white scarf for a meeting with the Pope.

Grand Duchess Maria Teresa of Luxembourg, Princess Marina of Naples, Queen Mathilde of Belgium, Queen Paola of Belgium, Queen Letizia of Spain and Queen Sofia of Spain are the other Catholic royals who are allowed to wear white when meeting with the pope.

Given her position, it's not known why Princess Charlene chose to wear black, but the mother-of-two - who has returned to Monaco after suffering from a mystery illness - looked stunning in a bespoke dress by Terrence Bray for the audience of her.

In 2016, Charlene used her privilege du blanc, wearing a white coat over a dress with white gloves and a lace veil.

She added black nail polish, a black lace scarf and a pearl rosary necklace with a gold cross to her look, along with heels from Louis Vuitton.

"I'm curious," wrote a royal fan on Twitter.

“Isn't she one of the few royals who can wear white?

It is not critical.

She looks beautiful."

Another fashion account shared the sentiment, posting photos from the event and asking: "I wonder why she didn't wear white since she has the privilege du blanc."