When the handsome Earl of Mornington visited Paris he became infatuated with her and, as the phrase went, 'contracted an alliance'. An actress, Hyacinthe was not the first nor the last young French
woman to become the mistress or wife of an Englishman.In 1784 Mornington brought her to live with him in England and took a house in Deanery Street, off Park Lane, where five children were born. As she was unable to speak English, she had only a restricted social life. Ten years after her arrival in England, they married but this did not alter the status of their children who remained illegitimate.

However, her husband wanted to become a Marquess with a special remainder to their eldest son, and, as well, that their daughters should be accorded the courtesy title of 'lady'. To his disappointment
he received his Marquessate, but only in the peerage of Ireland which he regarded as a "double gilt potato". For the rest of his life he continued to sigh for the dukedom he regarded as his proper reward;
but according to King George III, "If we make him a duke, he will be quite unbearable."

When her husband was Governor-General of India, she remained in England and the marriage did not survive his return. She was not only small-minded and jealous of his friends and political associates, but
while he was in India she accused him of infidelity though refused to join him. In 1805, while he was living at Apsley House, she moved out to live in Cumberland Place, on the north side of Hyde Park, and they were never to be reunited. However, as their children had grown up with her, her house became the family centre.
 

Source: Leo van de Pas