What was XXX's child's name?
Henrietta Ponsonby, Countess of Bessborough
Henrietta Ponsonby, Countess of Bessborough (16 June 1761 -- 11 November 1821), born Lady Henrietta Frances Spencer (generally called Harriet), was the wife of Frederick Ponsonby, 3rd Earl of Bessborough, and mother of the notorious Lady Caroline Lamb.
Lady Caroline Lamb