Question: Frances Shand Kydd's former husband was Viscount Althorp until when>

Context paragraphs:
Shand Kydd: Shand Kydd is an English surname.  It may refer to:

Peter Shand Kydd: Peter Shand Kydd (23 April 1925 – 23 March 2006) was the former stepfather of Diana, Princess of Wales, and an heir to the wallpaper fortune built by his father Norman Shand Kydd (1895–1962).  His mother was Francis Madalein Foy (died 1983).  He was half-brother to the former champion amateur jockey William Shand Kydd (1937–2014), who was brother-in-law of John Bingham, 7th Earl of Lucan.

Earl Spencer (peerage): Earl Spencer is a title in the Peerage of Great Britain that was created on 1 November 1765, along with the title Viscount Althorp, of Althorp in the County of Northampton, for John Spencer, 1st Viscount Spencer.  He was a member of the prominent Spencer family and a great-grandson of the 1st Duke of Marlborough.  Previously, he had been created Viscount Spencer, of Althorp in the County of Northampton, and Baron Spencer of Althorp, of Althorp in the County of Northampton, on 3 April 1761.

Lady Sarah McCorquodale: Lady Elizabeth Sarah Lavinia McCorquodale (née Spencer; born 19 March 1955) is the eldest daughter of John Spencer, 8th Earl Spencer, and the Hon. Frances Shand Kydd.  She is the sister of Diana, Princess of Wales.

Charles Spencer, 6th Earl Spencer: Charles Robert Spencer, 6th Earl Spencer, (30 October 1857 – 26 September 1922), styled The Honourable Charles Spencer until 1905 and known as The Viscount Althorp between 1905 and 1910, was a British courtier and Liberal politician from the Spencer family.  An MP from 1880 to 1895 and again from 1900 to 1905, he served as Vice-Chamberlain of the Household from 1892 to 1895.  Raised to peerage as Viscount Althorp in 1905, he was Lord Chamberlain from 1905 to 1912 in the Liberal administrations headed by Sir Henry Campbell-Bannerman and H. H. Asquith.  In 1910, he succeeded his half-brother in the earldom of Spencer.  He was married to Margaret Baring, a member of the Baring family.  They were great-grandparents of Diana, Princess of Wales.

Charles Spencer, 9th Earl Spencer: Charles Edward Maurice Spencer, 9th Earl Spencer, (born 20 May 1964), styled Viscount Althorp between 1975 and 1992, is a British nobleman, peer, author, print journalist, and broadcaster, and was the younger brother of Diana, Princess of Wales.  Through his sister, Spencer is the maternal uncle of Prince William, Duke of Cambridge and Prince Harry.

George Spencer, 2nd Earl Spencer: George John Spencer, 2nd Earl Spencer, (1 September 1758 – 10 November 1834), styled Viscount Althorp from 1765 to 1783, was a British Whig politician.  He notably served as Home Secretary from 1806 to 1807 in the Ministry of All the Talents.

John Shand Kydd: John "Johnnie" Shand Kydd (born in 1959) is an internationally exhibited photographer, the youngest son of Peter Shand Kydd and Janet Munro Kerr, and the stepbrother to Diana, Princess of Wales.  Kydd has exhibited at the National Portrait Gallery.

John Spencer, 8th Earl Spencer: Edward John "Johnnie" Spencer, 8th Earl Spencer, (24 January 1924 – 29 March 1992), styled Viscount Althorp until June 1975, was a British peer and the father of Diana, Princess of Wales.

Frances Shand Kydd: Frances Ruth Roche Shand Kydd (20 January 1936 – 3 June 2004) was the mother of Diana, Princess of Wales.  Her biographer, Max Riddington, who was the writer of "Frances: The Remarkable Story of Princess Diana's Mother", described Shand Kydd as a woman who was "certainly complicated" and also "funny, warm, intelligent, and energetic."  Following her divorce from Viscount Althorp in 1969, and Diana's death in 1997, Shand Kydd devoted the final years of her life to Roman Catholic charity work.

Supporting paragraphs: Frances Shand Kydd John Spencer, 8th Earl Spencer
Answer: June 1975