Born Harriett Sarah Moncreiffe in 1836, her parents were the Scottish baronet Sir Thomas Moncreiffe and Lady Louisa Hay-Drummond. On 6 December 1861 she married Sir Charles Mordaunt, who had inherited his father’s baronetcy in 1845, aged only nine. To mark his coming of age he had commissioned, for the enormous sum of £30,000, Sir George Gilbert Scott to rebuild Walton Hall, the family home, in exuberant Gothic style. From 1859 to 1868 he was the Conservative MP for South Warwickshire.
Sir Charles was a stolid country squire with no interests beyond hunting and shooting, and Harriet was a young beauty who had already caught the eye of the Prince of Wales. While Sir Charles killed foxes, deer, grouse, and salmon, or sat in Parliament, Harriet entertained numerous lovers, including the Prince and several of his aristocratic friends. In 1869 she gave birth to a blind daughter, Violet. Convinced that the baby’s affliction was the result of a venereal disease, Harriet confessed everything to her enraged husband.
Sir Charles immediately sued for divorce, threatening to name the Prince of Wales as a co-respondent. Harriet's father, who had several other daughters to marry off, announced that she was mad in order to prevent a divorce trial and save the family’s reputation. Harriet was incarcerated in various rented houses, and after some weeks either broke down or agreed to feign madness: smashing plates, eating coal, howling and crawling. The case was brought to court and the Prince of Wales was called as a witness; he admitted visiting Lady Mordaunt but nothing further was proved.
In 1875 Sir Charles sued again. Viscount Cole (later 4th Earl of Enniskillen), the father of Harriet's child, pled guilty to adultery with her and Sir Charles got his divorce. Harriet was kept in asylums for the rest of her life. However, her daughter Violet, sight restored, married the future Marquess of Bath.
Lady Mordaunt died on 9 May 1906.
Photographer unidentified.