Wikipedia
The House of Bourbon-Vendôme referred to two branches of the House of Bourbon. The first House of Bourbon-Vendôme was descended from Louis, Count of Vendôme (1376 – 1446), a cadet of the House of Bourbon-La Marche. Though a younger son, Louis was fortunate enough to receive Vendôme through his mother. Vendôme was raised to a duchy-peerage in 1515 in favor of Charles de Bourbon. By 1527, Charles had outlived the Dukes of Alençon and Bourbon, and became First Prince of the Blood. Charles' son Antoine became King of Navarre by marriage; his grandson Henry outlived the House of Valois in 1589, and succeeded to the French throne as the first of the Bourbon kings.
The second House of Bourbon-Vendôme descended directly from the first house. It was founded by César de Bourbon (1594–1665), the legitimized son of King Henry IV of France and his mistress, Gabrielle d'Estrées.