Born posthumously on 25 February 1753, daughter and sole heir of the Right Reverend Philip Twysden, Bishop of Raphoe, she was only seventeen years old when she married the seventeen-years older Earl of Jersey in the house of her step-father, General Johnstone. From this 
marriage ten children were born. 
Sir Herbert Croft wrote in 1780 of her "Beauty, Good-sense and Sweetness of Disposition", but added "Had she possessed more prudence with less vivacity; more affection with less inconstancy; more sincerity with less insinuation; she would have lived a pattern." Nevertheless her name was linked with the Prince of Wales (George IV) in 1782, though Lady Jersey professed having no feelings for the boy: "If he is in love with me I cannot help it. It is impossible for anyone to give another less encouragement than I have." 
By 1793 Lord Jersey was an elderly gentleman of the most courtly manners and fastidious dress. Known as the "Prince of Maccaronies" (sic), he held various appointments in the king's Household, while Lady Jersey was a friend of Queen Charlotte who listened with pleasure to her skilful playing of the harp. Mary Frampton described her as "clever, unprincipled, but beautiful and fascinating". By now she had made overtures to the nine-years-younger Prince of Wales who appreciated a woman of mature charm and undeniable beauty. 
At first the Prince of Wales abandoned Mrs. FitzHerbert for Lady Jersey but then realized he wanted them both. However, Mrs. FitzHerbert rejected his approaches but then gave in and restored her friendship with him. This was not to last for long, however, as George (IV) had decided to marry. Not knowing this and blaming Lady Jersey's influence, Mrs FitzHerbert went abroad. 
The marriage of the Prince of Wales and Caroline of Brunswick took place on 8 April 1795 but was doomed from the beginning as both took an instant dislike to the other. However, one contributary factor seemed to be his unconcealed preference for Lady Jersey. By 1796 King George III believed this marriage could still be salvaged if only Lady Jersey would retire from Court; at least, this was what the Princess of Wales made him believe. Determined not to lose her prince, Lady Jersey wrote a rude letter to Caroline and, far from breaking with her, the prince then spent more time with Lady Jersey than before. He even allowed her to move into a house next to his own "for the sake of Lord Jersey" as he assured his mother. 
Nevertheless, the marriage still broke down and his affaire with Lady Jersey lasted until about 1803, when her place in his affections was taken by Isabella, Lady Hertford, who in turn was to be replaced by Elizabeth, Marchioness Conyngham. 
On 22 August 1805, aged seventy, her husband Lord Jersey died suddenly, dropping dead while walking with his son near his son's house, Prospect Lodge, Tunbridge Wells. Queen Charlotte commented: "the poor deceased was never bad in himself, but weak and indulging to a little bewitching wife, which made him appear to some wanting in sense." 
As early as 28 August 1805, Henrietta, Lady Bessborough, describes a visit to the recently widowed Lady Jersey: "I went and found her really very ill, and very much affected; I expected it tho' everybody laughed at me for saying so, for she certainly used him very ill. I do not mean only in infidelities (Heaven knows, bad enough), but she made him unhappy---teased him and turned him into ridicule." 
Lady Jersey survived until 1821 when, after only two days' illness, she died at Cheltenham and was buried at Middleton Stoney. 
 

Source: Leo van de Pas