Emily FitzGerald, Duchess of Leinster

Emily FitzGerald, Duchess of Leinster , known before 1747 as Lady Emily Lennox, from 1747 to 1761 as The Countess of Kildare and from 1761 to 1766 as The Marchioness of Kildare, was the second of the famous Lennox sisters, daughters of Charles Lennox, 2nd Duke of Richmond, and illegitimately descended from King Charles II of England.

After the death of Lord Kildare in 1773, the Duchess caused a minor sensation by marrying her childrens tutor, William Ogilvie, with whom she had begun an affair some years earlier in Frescati House. Despite her remarriage she continued to be known as The Dowager Duchess of Leinster. Ogilvie was nine years her junior, and was the natural father of her youngest son from her first marriage. They lived for part of their marriage at Ardglass Castle in Ardglass, County Down, where Ogilvie worked to develop the village. A further three children were born to them after their marriage

Source: Wikipedia