In the year 1476, Duccio was engaged to Claudia Auditore da Firenze, Ezio's sister. However, he engaged in affairs with up to six other women at the same time, claiming that his father had told him he could "do much better than an Auditore.
After Claudia was informed of this by other girls, her brother Ezio met with Duccio outside the Duomo. There, he beat Duccio up as payback, and warned him to stay away from Claudia.
Ezio and Duccio met again in Rome while Duccio was in Rome for business. Ezio learned that Duccio was in possession of the three Leonardo da Vinci paintings which he was looking for. In their first meeting, Duccio spoke to Ezio rudely, saying how low he had fallen by living in Rome instead of "beautiful" Firenze. Ezio told him that they're not children anymore but he didn't listen and started taunting him about his sister and how she is now the "Madame of Roma". This infuriated Ezio and he punched him in the face. Duccio however stood up and, with the aid of his henchmen, engaged in a fist fight with Ezio. Ezio however defeated both Duccio and his henchmen. He forcefully asked him about the paintings and after getting his answer, he knocked him out cold.
Duccio reappeared for one last time in Constantiople in the year 1512. He was seen attempting to flirt with Sofia Sartor, much to her disgust. He was however been interrupted by Ezio again who became close to Sofia. Duccio, terrified of Ezio's presence, started to flee, crying to Sofia to run from the "devil".
In his later life, his business failed and he was left penniless. He barely survived, only just managing to scrape a living, and later died due to rabies, which he likely received from a dog bite.