During their long trips in northern Europe, Marchese Giacomo II Fagnani and his wife Costanza Brusati met in England Henry Herbert, 10th Earl of Pembroke, an English aristocrat well known for his amorous intrigues with Italian women.

On 25 August 1771 at the White's club of St James's, the Earl of March sent a letter to his friend George Selwyn (a prominent politician) that the previous night the Marchesa Fagnani gave birth a daughter named Maria Emilia, and that he was the father.

In the end, the Marchesa accepted, and allowed George Selwyn to appoint her daughter as heiress of his estate; in addition, the Earl of March (since 1778 Duke of Queensberry), one of the richest men in Britain, left much of his fortune to Maria Emilia when he died in 1810.

Despite her wealth, the Seymour-Conway family never accepted Maria Emilia due to her illegitimate origin, and in the end, this affected her marriage: after the birth of her last child, she moved to Paris, where she remained for the rest of her life.

The intricate custody battle for Mie-Mie and especially the controversial existence that she lived for many years in London and Paris had considerable echo in the aristocratic and upper-class society of her time.