In 1738, Pauline wrote to her elder sister, Madame de Mailly, the king's official mistress, asking to be invited to court. She received the invitation, and during her stay proceeded to seduce the king, who fell passionately in love with her.
Mademoiselle de Nesle then became the second official mistress of Louis XV, although her sister kept the position of maîtresse en titre. The king lavished her with gifts, the greatest being the castle of Choisy-le-Roi, newly decorated in blue and silver. To provide her an appropriate status at court, the king arranged for her to marry a nobleman only too pleased to leave the couple alone. On 28 September 1739, Mademoiselle de Nesle married Jean Baptiste Félix Hubert de Vintimille, marquis de Vintimille, comte du Luc (b. 1720), who departed to the country after their wedding. The new marquise de Ventimille soon became pregnant by the king.
Madame de Vintimille was described as graceful with a long, swan-like neck, but not beautiful. She was much more ambitious than her older sister and predecessor, Madame de Mailly, and possessed a great desire for money and political influence; her arrogance quickly made her hated within the court and by the people.
She could have been as politically influential as her two successors, Madame de Châteauroux and Madame de Pompadour, if not more, but her period as royal mistress was cut short; she died while giving birth to the son of the king in 1741.
Her corpse was placed at Lit-de-parade in the town of Versailles, but during the night the guards left the room to drink and a mob broke in and mutilated the corpse of "the king's whore".
Both the king and her older sister, Madame de Mailly, were deeply devastated by the death of their lover and sister, and Madame de Mailly is said to have begun to wash the feet of the poor as a Catholic sign of remorse.
The son of the king and Madame de Ventimille was named Louis after his father and given the title of duc de Luc. He so resembled his father that he was called Demi-Louis, "small Louis". He was raised by his aunt, Madame de Mailly. The king took care of his needs but never paid him much attention. Later, Madame de Pompadour wanted to marry her daughter to him, but the king would not allow it.