When did the first apparition of Our Lady of Guadalupe occur?

Our Lady of Guadalupe, also known as the Virgin of Guadalupe, is a Catholic title of Mary, mother of Jesus.

Catholic accounts provide that the Virgin Mary appeared four times to Juan Diego and once more to his uncle, Juan Bernardino. The first apparition occurred on the morning of Saturday, 9 December 1531 (Julian calendar, which is December 19 on the Gregorian calendar in present use), when it is said that an indigenous Mexican peasant named Juan Diego experienced a vision of a young woman at a place called the Hill of Tepeyac, which later became part of Villa de Guadalupe, in a suburb of Mexico City.

According to the accounts, the woman, speaking to Juan Diego in his native Nahuatl language (the language of the Aztec Empire), identified herself as the Virgin Mary, "mother of the very true deity".