Elena de Borbón y de Muguiro (1890-1910), daughter of Francisco de Borbón y Borbón, Duke of Marchena and of the duchess of Villafranca María del Pilar de Muguiro y Beruete. She died of tuberculosis when she wasn't yet 20!
Isabel Patino y de Borbón (1935-1954), daughter of the duchess of Dúrcal, a descendant of infante Sebastián Gabriel. She died soon after giving birth aged 19.
Orsetta Caracciolo (1940-1968), first wife of Marco Torlonia, cousin of King Juan Carlos.
Paul Alexandre Weiller (1971-1975) and his sister Laura Daphne Lavinia (1974-1980). Grandchildren of infanta Beatriz, daughter of Alfonso XIII. One of them died in a car accident the other one I can't recall.
María Mercedes (1880-1904) and María Teresa (1882-1912) de Borbón. sisters of Alfonso XIII they both shared the same tragic fate, dying young after giving birth.
Luis Alfonso de Baviera y Mesía (1942-1966), son of the infante José Eugenio de Baviera y Borbón, himself a grandson of Alfonso XII. He died in a car wreck.
Alfonso Márquez y Patino (1936-1994), Marquis of Castro, brother-in-law of the previous as he was married to María Teresa de Baviera y Mesía. He also died in a car wreck.
Alfonso Carlos de Borbón y Habsburgo-Lorena (1849-1936), Carlist pretender, son of Carlist King Juan III and Beatriz of Austria-Este. He died after having been ran over by a car.
María de la Paz de Borbón y Borbón (1862-1946), daughter of Isabel II, she died after falling from the stairs.