Lady Bessborough (1761-1821) was born Henrietta Frances Spencer (known always as Harriet) and became Countess of Bessborough in 1780 when she married Frederick Ponsonby.
Lady Granville Leveson-Gower (1785-1862), the niece of Lady Bessborough, was born Lady Harriet Cavendish and became Countess Granville on her marriage to Lord Granville Leveson-Gower in 1809. On marrying, Lord Granville terminated his relationship with Lady Bessborough.
Countess Granville's letters, edited by her son, were published in 1894 under the title:
Letters of Harriet, Countess Granville (1810-1845) edited by Edward F. Leveson-Gower.