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Csar de Bourbon, Lgitim de France was the son of Henry IV of France and his mistress Gabrielle dEstres, and founder of the House of BourbonVendome. He held the titles of 1st Duke of Vendme, 2nd Duke of Beaufort and 2nd Duke of tampes, but is also simply known as Csar de Vendme. Through his daughter, lisabeth de Bourbon, Csar was a greatgreatgreatgrandfather of Louis XV of France, merging thereafter to the French royal line. Csar de Bourbon is also an ancestor of Juan Carlos I of Spain, of Albert II, King of the Belgians, of Henri, Grand Duke of Luxembourg, and of Vittorio Emanuele, Prince of Naples, a pretender to the Italian throne.
He was his fathers first son but due to his illegitimacy, was not allowed to inherit the throne his half brother, the future Louis XIII of France was born in September 1601 much to the joy of the king.
Source: Wikipedia