Francesco was a son of an aristocrat that met Leonardo when he was 15 and stayed with him almost his entire life. From 1506-1517 he also Inherited much of Leonardo's estate and works.
"Melzi himself, in a letter, described Leonardo's feelings towards him as a sviscerato et ardentissimo amore ("a deeply passionate and most burning love"). Salai eventually accepted Melzi's continued presence and the three undertook journeys throughout Italy. Melzi became Leonardo's pupil and life companion, and is considered to have been his favorite student.
"He accompanied Leonardo on trips to Rome in 1513 and to France in 1517. As a painter, Melzi worked closely with and for Leonardo. Some works which, during the nineteenth century, were attributed to Leonardo are today ascribed to Melzi.
Upon Leonardo's death, Melzi inherited the artistic and scientific works, manuscripts, and collections of Leonardo, and would henceforth faithfully administer the estate.
Returning to Italy, Melzi married, and fathered a son, Orazio. When Orazio died on his estate in Vaprio d'Adda, his heirs sold the collection of Leonardo's works."