When Denmark's Crown Prince Frederik and Crown Princess Mary welcomed twins in 2011, the proud dad joked he might name his new son Elvis as she shared a birthday with the King of Rock and Roll. The actual pick was no less of a surprise. Vincent gets his name all to himself in royal circles. It's a more popular choice in Australia, his mum's home country, but if we're honest, we're all still getting used to a prince called Vince.