Dom Sebastian Gabriel of Bourbon and Braganza, (Rio de Janeiro, 4 November 1811 – Pau, 14 February 1875) Infante of Portugal and Spain, was a royal of the 19th century, progenitor of the ducal lines of Hernani, Ansola, Dúrcal and Marchena, and Carlist army commander in the First Carlist War.

He was born in Rio de Janeiro in 1811 as the only child of Infanta Maria 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.

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.

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