Question: When did Margaret Georgiana Spencer's husband die?

Context articles: Georgiana Cavendish, Duchess of Devonshire
Henrietta Ponsonby, Countess of Bessborough
Georgiana Spencer, Countess Spencer
John Spencer, 1st Earl Spencer
Louisa Hamilton, Duchess of Abercorn
Georgiana Howard, Countess of Carlisle
Harriet Leveson-Gower, Countess Granville
Poor Servants of the Mother of God
Georgiana Burne-Jones
Georgiana Rolls, Baroness Llangattock

Georgiana Cavendish, Duchess of Devonshire ("née" Spencer; ; 7 June 1757 – 30 March 1806) was an English socialite, style icon, author, and activist.
 Of noble birth from the House of Spencer, married into the House of Cavendish, she was the first wife of William Cavendish, 5th Duke of Devonshire, and the mother of the 6th Duke of Devonshire.
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.
 Her father, John Spencer, 1st Earl Spencer, was a great-grandson of John Churchill, 1st Duke of Marlborough.
 Her sister was Georgiana Cavendish, Duchess of Devonshire.
Margaret Georgiana Spencer, Countess Spencer ("née" Poyntz; 8 May 1737 – 18 March 1814), was an English philanthropist.
 She was born at St James's Palace as the daughter of a diplomat and a maid of honour to Caroline of Ansbach.
 In 1754, she married John Spencer, one of the wealthiest men of the era.
 A love match, the marriage resulted in the births of three surviving children, which included Georgiana Cavendish, Duchess of Devonshire.
 The Spencers became earl and countess in 1765, a reward granted by the Duke of Newcastle for John's political loyalty to the Whig party.
John Spencer, 1st Earl Spencer (19 December 1734 – 31 October 1783) was a British peer and politician.
Louisa Jane Hamilton, Duchess of Abercorn, VA (née Lady Louisa Jane Russell) (8 July 1812 – 31 March 1905) was the wife of James Hamilton, 1st Duke of Abercorn, and the daughter of John Russell, 6th Duke of Bedford, by his second wife, Lady Georgiana Gordon.
 She was the mother of Louisa Montagu Douglas Scott, Duchess of Buccleuch, and therefore the paternal great grandmother of Princess Alice, Duchess of Gloucester, and the maternal 2nd great-grandmother of Prince William of Gloucester and Prince Richard, Duke of Gloucester.
 She was also the mother of James Hamilton, 2nd Duke of Abercorn, and therefore the paternal great-grandmother of Cynthia Spencer, Countess Spencer, and the paternal 3rd great-grandmother of Diana, Princess of Wales, and the maternal 4th great-grandmother of Prince William, Duke of Cambridge, and Prince Harry.
 Through her daughter Lady Louisa Hamilton she also is the maternal 3rd great-grandmother of Sarah, Duchess of York.
Georgiana Dorothy Howard, Countess of Carlisle ("née" Cavendish; 12 July 1783 – 8 August 1858) was a British noblewoman.
 She was born after nine years of childless marriage between William Cavendish, 5th Duke of Devonshire and his wife Lady Georgiana Spencer, the political hostess and socialite.
 As such, she was a member of one of the country's grandest and richest families.
Henrietta Elizabeth "Harriet" Leveson-Gower, Countess Granville ("née" Cavendish; 29 August 1785 – 25 November 1862) was a British peeress and society hostess.
 She was born in Devonshire House as the second daughter of William Cavendish, 5th Duke of Devonshire by his wife, the political hostess Lady Georgiana Spencer.
 Despite her parents' turbulent marriage, Harriet had a happy childhood.
 Her mother's death in 1806 led to an unpleasant situation in which her father's long-time mistress Lady Elizabeth Foster took control of the Devonshire household; as the unmarried eldest daughter, this should have been Harriet's role.
The Poor Servants of the Mother of God are a religious congregation founded in 1872 by the venerable Mother Mary Magdalen of the Sacred Heart, Frances Margaret Taylor.
 She was closely assisted by her friend and benefactor Lady Georgiana Fullerton, and following her death, by her husband, Mr A G Fullerton (1808-1907).
Georgiana Burne-Jones, Lady Burne-Jones (Birmingham, 21 July 1840 – 2 February 1920), the second oldest of the Macdonald sisters, was the wife of Pre-Raphaelite Brotherhood artist Edward Burne-Jones, mother of painter Philip Burne-Jones, confidant and friend of William Morris and George Eliot, and something of a painter and engraver in her own right.
 She was a Trustee of the South London Gallery and was elected to the parish Council of Rottingdean, near Brighton in Sussex.
 She is known for the biography of her husband, "The Memorials of Edward Burne-Jones" and for publishing his "Flower Book".
 She became the mother-in-law of John William Mackail, who married her daughter Margaret.
 Their children were the novelists Angela Thirkell and Denis Mackail.
Georgiana, Lady Llangattock, (28 February 1837 (baptised) – 1 April 1923), born Georgiana Marcia Maclean and after her marriage termed Georgiana Marcia Rolls, was a socialite, benefactor and an enthusiast for Horatio Nelson and associated naval heroes.
 She was the wife of John Rolls, 1st Baron Llangattock, a Victorian landowner, Member of Parliament and agriculturalist.
 She and her husband lived at The Hendre, a Victorian country house north of Monmouth.