Leonardo had 12 half-siblings

Piero's legitimate heirs were born from his third wife Margherita di Guglielmo, who gave birth to six children, and his fourth and final wife, Lucrezia Cortigiani, who bore him another six heirs. In all, Leonardo had 12 half-siblings, who were much younger than he was (the last was born when Leonardo was 40 years old) and with whom he had very little contact.