Giulia Farnese (1474 – 23 March 1524) was mistress to Pope Alexander VI, and the sister of Pope Paul III. She was known as Giulia la bella, meaning "Julia the beautiful" in Italian.
Lorenzo Pucci described her as "most lovely to behold". Cesare Borgia, the son of Alexander VI, described her as having "dark colouring, black eyes, round face and a particular ardor".
Giulia Farnese was born in Canino, Latium, Italy. Her parents were Pier Luigi Farnese, Signore di Montalto (1435–1487), and his wife Giovanna Caetani. One earlier member of this dynasty had been Pope Boniface VIII (1294–1303). She had four siblings. Her oldest brother, Alessandro, was a notary who embarked on an ecclesiastical career. Her second brother, Bartolomeo, became Lord of Montalto in Alessandro's place, married Iolanda Monaldeschi, and had issue. Her third brother, Angelo, was a lord who married Lella Orsini and had female issue. The fourth sibling was a sister, Girolama.
On 21 May 1489, she married Orsino Orsini in Rome (the signing of the marriage contract had taken place the previous day). Her dowry for the match was 3,000 gold florins (around US$500,000). Orsini, who was described as being squint-eyed and devoid of any meaningful self-confidence, was the stepson of Adriana de Mila. Adriana de Mila was a third cousin of Cardinal Rodrigo Borgia, who was then Vice-Chancellor of the Church. According to Maria Bellonci, it is uncertain when Rodrigo Borgia (Pope Alexander VI) fell in love with Giulia and decided to make her his mistress. What is known is that Adriana de Mila eventually gave her approval to Rodrigo Borgia and Giulia Farnese's relationship in order to win a higher status for her son within the Vatican. By November 1493, Giulia was living with Adriana de Mila and the Pope's daughter Lucrezia Borgia in a recently built palace next to the Vatican from where the Pope could easily make his clandestine visits. The affair was widely rumored among gossips of the time, and Giulia was referred to as "the Pope's whore" or sarcastically as "the bride of Christ". Giulia and Lucrezia became close friends.