Lady Elizabeth Cavendish
Lady Elizabeth Georgiana Alice Cavendish ( 24 April 1926 – 15 September 2018 ) was a British noblewoman who was a childhood friend of Queen Elizabeth II and a lady-in-waiting to Princess Margaret from the late 1940s until the latter's death in 2002 . 
<triplet> Queen Elizabeth II <subj> Princess Margaret <obj> sibling