First up, is Mary Darby Robinson, the English Sappho and the Prince Regent's first publicly known mistress. She was a poet, actress and an early feminist.
Elizabeth Milbanke Lamb, the Viscountess Melbourne, is as famous for being the Prince Regent's mistress as she is for being a confidante to Lord Byron with whom she exchanged letters while he was in exile though she was nearly forty years his senior.
Mrs Maria Smythe Weld Fitzherbert, the most notable mistress of the Prince Regent. The two married in the autumn of 1785, but the marriage was not considered legal under the Royal Marriage Act of 1772.
Frances Villiers, the Countess of Jersey and one of the more notorious of the Prince Regent 's Mistresses. She was said to have encouraged him to marry poor Caroline in order to secure her own position at his side and did so to success for over a decade. She headed the prince's household though he was married to Caroline until she was replaced by Isabella Ingram-Seymour-Conway, Marchioness of Hertford.