He inherited the Carlist pretensions to the Spanish throne of his brother Archduke Karl Pius and called himself Duke of Madrid.

His father, a member of the Tuscan line of the Habsburg family and thus a descendant of Emperor Leopold II, had been Inspector General of the Austrian Artillery and Commander of the 18th infantry regiment.

The family's main residences were the Palais Toskana in the district of Wiede in Viena and Schloss Wilhelminenberg, on the Eastern slopes of the Gallitzinberg.

Due to World War I, Franz Josef was not educated by private tutors like his three eldest brothers had been, but was sent instead to Stella Matutina, a Catholic school for boys run by Jesuits priest in Feldkirch.

[4] His two eldest brothers, Archdukes Rainer and Leopold, decided to remain in Austria and recognized the new republic.

[5] In 1926, Archduke Franz Josef officially became a Spanish citizen with the name Francisco José Carlos de Habsburgo y Borbón.

He initially lived with his widowed mother and his unmarried siblings, Archduchess Dolores and Archduke Karl Pius of Austria, Prince of Tuscany.

[7] While on a visit to Berlin, he fell in love with an Austrian emigre, Marta Baumer, who had divorced Baron von Kahlera, a wealthy Czech sugar exporter.

[8] With his mother's approval, Archduke Franz Joseph married Martha Baumer in London on 22 July 1937.