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Family

• He was born in Rio de Janeiro in 1811 as the only child of Infanta Teresa, Princess of Beira and Infante Pedro Carlos of Spain and Portugal. His mother was the eldest daughter of King John VI of Portugal (and also a granddaughter of King Charles IV of Spain); and his father, who died before Sebastian was born, was a male-line grandson of King Charles III of Spain as well as a female-line grandson of the Queen regnant Maria I of Portugal and Brazil. Sebastian was soon granted the title of Infante of Portugal and Brazil. However, because he was quite a distant descendant (great-grandson) in male line of any Spanish monarch, he was not Infante of Spain from birth.

However in 1824 he was granted also the style of Infante of Spain by his maternal granduncle King Ferdinand VII of Spain.

Civil War

• In Portugal, the country was in effective civil war since 1826, when "usurper-king" Miguel I of Portugal and his elder brother Pedro IV of Portugal (both were uncles to Sebastian) battled, until 1834.
• Sebastian's mother remarried two decades later, in 1838, her uncle, Infante Carlos, Count of Molina, the first Carlist pretender of Spain. Teresa had been Carlist supporter since the succession dispute started in 1833, and spent her time in Carlist camp, usually in northern Spain.
• Sebastian participated in the second siege of Bilbao and became commander of the Carlist Army of the North from December 30, 1836. He won the Battle of Oriamendi (March 16, 1837) against the British Legion under George de Lacy Evans. Then he led the failed Royal Expedition against Madrid and was sacked upon its return to the north in late 1837.

Titles, Marriage and Children

• On January 15, 1837, in midst of the First Carlist War, the then 23-year-old Sebastian was excluded, by law of the Cortes, ratified by royal decree of Regent Maria Christina, from the Spanish succession, on grounds of his being rebel against Isabella II of Spain with Don Carlos' rebellion. Sebastian was also declared to be stripped from his Spanish titles and status as a dynast.
• The same exclusion was legislated also to Don Carlos, Carlos' sons, and Sebastian's uncle the deposed Miguel I of Portugal, as well as to Sebastian's mother Teresa.
• Much later, in 1859, Sebastian was restored to his Spanish titles, in conjunction with his second marriage. He returned to Spain from Naples where he had lived since the eind of the war in 1839.
• Firstly Sebastian had married to his cousin Princess Maria Amalia of Bourbon-Two Sicilies but the marriage, which lasted several decades, remained childless.

When widowed at the age of 50, he remarried on November 19, 1860, this time to his cousin Infanta Maria Cristina of Spain, decades his junior. They produced three surviving sons, who were each granted their own dukedoms.

Some information on their children:

• Francisco, duke of Marchena (Madrid, 1861 – Neuilly-sur-Seine, 1923). He married María del Pilar de Muguiro y Beruete, duchess of Villafranca.
• Pedro d'Alcantara, duke of Dúrcal (Madrid,1862 – París, 1892). He married María de la Caridad de Madán y Uriondo.
• Luíz, duke of Ansola (Madrid, 1864 – Algier, 1889). He married María Ana Bernaldo de Quirós y Muñoz, marquise of Atarfe.
• Alfonso (Madrid, 1866 – Madrid, 1934).
• Gabriel (Pau, 1869 – Madrid, 1889).
• The last head of one of these branches, the duke of Hernani, adopted in 1970's their distant cousin, Infanta Margarita of Spain, Duchess of Soria who thus became the next and current Duchess of Hernani.
• After the overthrow of Isabella II of Spain in 1868 he moved to Pau, where he tried to reconcile the Carlist and Isabeline branches of the House of Bourbon, without success.