The Cartier timepiece in question was purchased for Princess Margaret by the Queen Mother, wife of King George VI. The art deco style watch was purchased for the Princess by her mother on the occasion of her 20th birthday in 1940.
From Her Majesty's Jewel Vault: Queen Victoria's Crown Ruby Brooch purchased along w/ necklace & earrings, from Garrard in 1854 by QV. Worn by Queen Elizabeth, Queen Mother with rest of parure & Oriental Circlet Tiara. Not seen since death in 2002. Worn firstly by QEII on 6/16/2015 to 2015 Royal Ascot Day. http://queensjewelvault.blogspot.com/2015/06/queen-victorias-crown-ruby-brooch.html
.Princess Louise Margaret of Prussia (25 July 1860 - 14 March 1917) - German princess, and later a member of the British royal family. March 13, 1879, Louise Margaret married Arthur William Patrick, Duke Konnautskogo and Straharnskogo. After the ceremony, Louise Margaret received the title of "Her Royal Highness the Duchess of Konnautskaya and Straharnskaya"