Francis III of Brittany 1518-1536, Duke of Brittany and Dauphin of Viennois.
He was the son of the French King Francis I and of Claude de France, Duchess of Brittany. In his capacity as eldest son and presumed heir to the throne, he bore the title Dauphin or, more precisely, Dauphin of Viennois. François was baptized on 25 April 1519 in Amboise, the decorations for the baptismal ceremony were created by Leonardo da Vinci.
Duke Franz III died at the age of eighteen, eleven years before his father, on August the 10th 1536 at Tournon Castle on the Rhone, after drinking a glass of water. His brother Henri succeeded him as heir to the throne and Duke of Brittany.
Count Montecuccoli, his secretary, was accused of poisoning him in the service of Emperor Charles. During a search of his quarters various poisons were found and he confessed to murder under torture. Among historians, however, the thesis of death by poison is controversial.
Source: “Modes et Costumes Historiques“. Drawing by Xavier Willemin. Edited and steel engraving by Hippolyte Louis Emile and Polidor Jean Charles Pauquet. Published by Cassell, Petter & Galpin London, 1864