the Countess of Derby, and briefly (c. 1784) with Lady Elizabeth Foster, daughter of Frederick Hervey, 4th Earl of Bristol and mistress of William Cavendish, 5th Duke of Devonshire. The first affair was notable because it did not lead to a divorce. The Countess of Derby was born Lady Elizabeth Hamilton, the only daughter of the 6th Duke of Hamilton and the beauty Elizabeth Gunning. However, the Earl of Derby refused to divorce his errant wife. This meant that Lady Derby was ostracized for the remainder of her life, and Dorset soon lost interest and abandoned his lover. He was received back into society, and even received by his former mistress's betrayed husband Lord Derby. Marriage and descendants In 1790, after returning from France, Dorset married twenty-three-year-old Arabella Diana Cope (1767–1825), daughter and co-heiress of Sir Charles Cope, 2nd Baronet, and stepdaughter of Charles Jenkinson, 1st Earl of Liverpool. Dorset and Arabella had one son together, George John Frederick, who was born on 15 November 1793, and two daughters, Lady Mary Sackville, born on 30 July 1792, and Lady Elizabeth Sackville, born on 11 August 1795. The Duke died in 1799, aged 54, and left a life interest in his estates and free disposition thereof (in case of the death of their young son) to his wife. At his death, Arabella was thus a very wealthy heiress and from 1799 until her own death in 1825, Arabella, Duchess of Dorset (as she preferred to be known) controlled the Sackville estates and wealth in trust for their son. She remarried 1801 Charles Whitworth, who became 1st Earl of Whitworth, but had no further issue. George John Frederick became the 4th Duke of Dorset on his father's death at the family seat, Knole House, near Sevenoaks, Kent at age 6, but spent the rest of his life under the legal and financial control of his mother and stepfather. He died in a riding accident in Ireland, aged 21 having just become engaged to Lady Elizabeth Thynne (born 1795), elder daughter of Thomas Thynne, 2nd Marquess of Bath. (She went on to marry October 1816 Lord Cawdor and have many children). Although the dukedom passed to his cousin Charles, Viscount Sackville, the estates remained at the disposition of Arabella until her own death in 1825, when Knole went to her elder daughter Mary, Countess of Plymouth, and Buckhurst and the Middlesex lands (of