His father had been dead for seventeen days when she gave birth to him. She was just twenty. The King of France had arranged their marriage. She had already borne the king a daughter. On paper, that child belonged to two people who did not exist.

Marie-Louise O'Murphy was born in Rouen on 21 October 1737 and baptised that same day in the parish church of Saint-Éloi. Her father was Daniel Morphy, her mother Marguerite Iquy. Both their names went into the register. The family was of Irish origin, established in Normandy, and Marie-Louise was the youngest of twelve children. Before she was seventeen, the same ordinary business of naming a child's parents would become something considerably less straightforward.

She was about fifteen when she became Louis XV's mistress. He was in his forties. Around them stood the adults who arranged access to the king, provided accommodation and dealt with the consequences. Marie-Louise was installed in a house in the Parc-aux-Cerfs district of Versailles, close to the palace but outside its public life. Madame de Pompadour remained the established favourite. There was room in the king's arrangements for a teenage girl without there being a place for her beside him at court.

The Boucher paintings traditionally associated with her have made her youth much more visible than the rest of her life. That life included pregnancies, marriages, children and a widowhood before she had been an adult for very long.

In 1754, at sixteen, Marie-Louise gave birth in Paris to Agathe-Louise. At the child's baptism in Saint-Paul, the father was entered as Louis Saint-André, a former infantry officer. The mother was Louise-Marie de Berhini, living in the rue Saint-Antoine. An occupation, an address, two parental names: the entry supplied the appearance of an ordinary family. Neither named parent was the actual parent. The king and the girl who had given birth were both absent from it.

The paperwork was more discreet than the court.

Agathe-Louise was placed with a wet nurse and later brought up at the convent of the Présentation. The king paid for her upbringing, and trusted men acted as her guardians. Provision was made for the child. It was possible to arrange her maintenance, her education and eventually her marriage while keeping her actual parents out of her baptismal identity. None of those arrangements required her mother's name.

By November 1755, the royal relationship was over. Marie-Louise, newly eighteen, was married to Jacques de Beaufranchet, seigneur d'Ayat, an army officer from an Auvergne noble family. The king supplied a dowry of 200,000 livres, disguised as a gift from elsewhere. The marriage brought Jacques money and Marie-Louise a recognised position in provincial noble society.

Her name received attention too. For the marriage she became Morphy de Boisfailly, presented as the daughter of an Irish gentleman. A family respectable enough for the match could be supplied on paper, just as an unremarkable family had been supplied for her daughter. Versailles had considerable experience in making awkward circumstances presentable.

At Ayat, Marie-Louise began another family. A daughter, Louise Charlotte, was born in October 1756. The following year she was pregnant again while Jacques served in the French army. The Seven Years' War took him to Saxony, where, on 5 November 1757, he was killed at the Battle of Rossbach.

On 22 November, at Ayat, Marie-Louise gave birth to Louis Charles Antoine de Beaufranchet. This time the father's name could be entered truthfully.

She had turned twenty a month earlier.

The marriage arranged after her dismissal had lasted less than two years. There was a small daughter as well as the newborn son, and beyond that household there was Agathe-Louise, growing up under the arrangements made for the king's child. Marie-Louise had acquired money and rank. Neither had spared her an early widowhood.

Louise Charlotte died in February 1759, aged two. Thirteen days later, at Riom, Marie-Louise married François Nicolas Le Normant de Flaghac. Another daughter, Marguerite-Victoire, was born during the second marriage in 1768. Marie-Louise's life continued among families and fortunes well beyond the few years for which she is usually remembered.

There was real wealth in those later years. In 1782, she and her second husband acquired Migneaux, near the Seine at Villennes. The salon was furnished with carved and gilded chairs and sofas covered in blue damask, and the household silver was valued at more than 10,000 livres. Her signature survives on the purchase document. Here was another record bearing her name, attached now to property. When François Nicolas died in 1783, she was widowed for a second time; she sold Migneaux in 1785.

Agathe-Louise had already died in 1774, aged twenty, within a year of her marriage. Marie-Louise lived on into the Revolution, and in February 1794 she was arrested as a suspect and held in Paris prisons until the fall of Robespierre set her free. She lived through the Empire and into the restoration of the Bourbons. The girl whose first child had been registered under an invented mother's name grew old, and her daughter Victoire had a Paris household of her own. Marie-Louise died there on 11 December 1814, aged seventy-seven. Sixty years after the birth of the king's daughter, she ended her life in another daughter's home.