According to the Royal Forums:
The Prince of Wales and the Duchess of Cornwall had a private audience with Pope Francis on Tuesday as part of their week-long tour of Europe.
In a sign of changing times at the Vatican, the Duchess did not wear black or a mantilla, as has been usual tradition for non-Catholic female royals in the past. Instead, she looked elegant in a gold frock from her favourite designer, Anna Valentine, accessories with a matching scarf and pearl jewellery.
Vatican Library and Secret Archives…[showed them] a number of documents from the 1500s that link England and the Catholic Church.