Henrietta Harley, Countess of Oxford and Countess Mortimer was an English noblewoman, the only child and heiress of John Holles, 1st Duke of Newcastle and his wife, the former Lady Margaret Cavendish,
Henrietta Harley, Countess of Oxford and Countess Mortimer (1694–1755), by John Wootton
Margaret Cavendish Bentinck, Duchess of Portland was the richest woman in Great Britain of her time, styled Lady Margaret Harley before 1734, Duchess of Portland from 1734 to her husband's death in 17
Henrietta Harley, Countess of Oxford and Countess Mortimer
…to her husband. They had two children. Their son, Henry Cavendish Harley, Lord Harley, lived only four days. Their only child to attain maturity was Margaret (1715–1785), and so whilst Margaret inherited most of the combined Holles-Harley fortunes on her parents' deaths, the title of Earl of Oxford and Earl…
Margaret Cavendish Bentinck, Duchess of Portland by Christian Friedrich Zincke, 1738
Portrait c. 1744 by Thomas Hudson