Next stop: Belgrade. Crown Prince Alexander of Serbia (formerly Yugoslavia) is son of a king but heir to a kingdom that no longer exists -- the monarchy long since abolished in his homeland.

The Dutch royal family were out in full force on Saturday for King Willem-Alexander's 57th birthday, and Crown Princess Catharina ... including Prince Pieter-Christiaan, Princess Laurentien ...

Queen Mary and King Frederik of Denmark reunited with their son Crown Prince Christian over the weekend. Their Majesties and their younger children, Princess Isabella, Prince Vincent and Princess ...