The royal turned to one of her favourite designers Terrence Bray for a bespoke dress, stepping out for the poignant occasion in a boundary-breaking ensemble. Complete with a bateau neckline, structured A-line skirt and sheer long sleeves, Princess Charlene's knee-skimming boat dress was paired with a rosary bead necklace and black lace mantilla.
WATCH: Fashion rules royal ladies have to follow
Traditionally, it is protocol for women to wear a long-sleeved black garment and black veil during a meeting with the Pope, believed to signify the virtues of piety and humility - so why did Princess Charlene's outfit leave fans confused?
The mother-of-two actually has 'privilège du blanc', a Catholic custom whereby certain designated queens, queen consorts and princesses are permitted to wear a white dress and veil during audiences with the Pope.
Princess Charlene wore a bespoke dress designed by Terrence Bray
Princess Charlene is one of just seven women in the world who are permitted to wear white garments. She shares the privilege with the Queens of Spain, Belgium and Italy, the Grand Duchess of Luxembourg, and the Princesses of the House of Savoy.
Royal fans were divided over her daring outfit choice, rushing to react in the comments sections of Instagram account @royalfashionpolice.
"Still elegant and dignified, but I wonder why she didn’t choose to wear white?" asked one fan, while another penned: "Love this! Shoulders mostly covered but edgy, the veil is stunning, and the necklace isn’t quite a rosary. Pushing boundaries, but elegant."
"A surprising choice of neckline for the Vatican," wrote another, as a fourth comment read: "Charlene looks lovely, however she is pushing it with bare shoulders at an audience with the Pope."
The royal formerly met with Pope Francis in 2016
It's the first time Princess Charlene has chosen not to use her privilège du blanc, having worn white to two previous meetings at the Vatican.
She wore white during an audience with Pope Benedict XVI in 2013 and with Pope Francis previously in 2016, styling a far more conservative outfit consisting of a structured white blazer, lace veil and white gloves.
Make sure you never miss a ROYAL story! Sign up to our newsletter to get all of our celebrity and royal news delivered directly to your inbox.