I thought at first it was restricted to only Catholic queens. But it seems that it extends to Catholic grand duchesses as well. I was surprised to see Charlene of Monaco wearing white at the inauguration mass of Pope Leo XIV: so I'm assuming that this privilege extends to Catholic princesses who are either sovereigns or consorts of sovereigns.

The article I read stated that at present, only seven women in the world can wear white in the presence of the pope: I'm assuming that they are Queens Paola and Mathilde of the Belgians, Queens Sofia and Letizia of Spain, Queen Maxima of the Netherlands, Grand Duchess Maria Teresa of Luxembourg, and Princess Charlene of Monaco.

Once Hereditary Grand Duke Guillaume ascends the throne of Luxembourg, Stephanie will be eligible for this privilege, like her mother-in-law. However, as long as the widowed Prince Hans-Adam II of Liechtenstein is living, his daughter-in-law Sophie CANNOT wear white in the presence of His Holiness -- correct? It doesn't matter that he has delegated ruling powers to his son and heir, Hereditary Prince Aloys, as regent of the principality: he remains the official sovereign.

Can anybody explain the precise reason or basis for the white privilege, anyway? Does it have anything to do with Queen Isabel I of Castile ("Isabel la Catolica")?