The current titular Duke of Parma and Piacenza is the son of princess Irene of the Netherlands. So he is a maternal grandson of Queen Juliana of the Netherlands. His mother had to give her place in the line of succession to the Dutch throne when she married his father.

Infante Felipe of Spain, Duke of Parma married Louise Elisabeth de France eldest daughter of Louis XV of France and Navarre.
Their oldest daughter princess Isabella of Parma was the first wife of Emperor Joseph II.
Her sister Maria Luisa became the wife of Carlos IV of Spain.
Their brother Ferdinand was married of to Archduchess Maria Amalia of Habsburg-Lorraine.

Louise d'Artois, granddaughter of Charles X of France and Navarre and sister to Henri count of Chambord became the mother of Roberto I the last reigning duke who fathered 12 children each with both his wives. His second wife was a Portuguese Infanta and sister to Grand Duchess Maria Anna of Luxembourg, mother of grand duchess Charlotte who married her first cousin Felix.

Felix' oldest half sister married Ferdinand I of Bulgaria and was the mother of king Boris.

Princess Maria Pia of Savoye the eldest daughter of king Umberto II of Italy and his queen Marie Jose of Belgium was first married to a prince of Yugoslavia but after her divorce married her long standing partner prince Michel of Bourbon-Parma. There has been speculation that he might also be the biological father of her second set of twins.