Elizabeth Christiana Cavendish, Duchess of Devonshire (13 May 1758 – 30 March 1824) was an English aristocrat and letter writer. She is best known as Lady Elizabeth Foster, the close friend of Georgiana Cavendish, Duchess of Devonshire. Elizabeth supplanted the Duchess, gaining the affections of William Cavendish, 5th Duke of Devonshire and later marrying him. Several of her letters are preserved. Life Known as Bess, she was born Elizabeth Christiana Hervey on 13 May 1758, in a small house in Horringer, St Edmundsbury, Suffolk. Her father, Frederick Hervey, Bishop of Derry, later became the fourth Earl of Bristol. She had three brothers, including John, Lord Hervey and Frederick, 1st Marquess of Bristol; and two sisters, Lady Mary Erne and Louisa, Countess of Liverpool. In 1776, Elizabeth married Irishman John Thomas Foster (1747–1796). He was a first cousin of the brothers John Foster, last Speaker of the (united) Irish House of Commons, and Bishop (William) Foster. The Fosters had two sons, Frederick (3 October 1777 – 1853) and Augustus John Foster (1780–1848). Their only daughter, also named Elizabeth, was born prematurely on 17 November 1778 and lived only eight days. When her father succeeded as the earl in 1779, she became Lady Elizabeth Foster. The couple resided after 1779 with her parents at Ickworth House in Suffolk. The marriage was not a success, and the couple separated within five years, after Bess received reports of an "intrigue" between Foster and her maid, Madam Wagniere. Despite knowing that she would be destitute, Bess wrote to Foster, "it is my fixt wish & determination not to return to you." Foster retained custody of their sons and did not allow the boys to see Bess for 14 years. In May 1782, Bess met the Duke and Duchess of Devonshire in Bath, and quickly became Georgiana's closest friend. From this time, she lived in a triad with Georgiana and her husband, William, the 5th Duke of Devonshire, for about 25 years. She bore two illegitimate children by the Duke: a daughter, Caroline St Jules, and a son, Augustus (later Augustus Clifford, 1st Baronet), who were raised at Devonshire House with the Duke's legitimate children by Georgiana. Georgiana grew ill and died in 1806; three years later, Bess married the duke and became the Duchess of Devonshire. He died two years later. Bess is also said to have had affairs with several other men, including Cardinal