Princess Margaret , Countess of Snowdon ( Margaret Rose ; 21 August 1930 -- 9 February 2002 ) , was the younger daughter of King George VI and Queen Elizabeth , and the only sibling of Queen Elizabeth II .
Princess Margaret , Countess of Snowdon CI GCVO GCStJ ( Margaret Rose ; 21 August 1930 -- 9 February 2002 ) , was the only sibling of Queen Elizabeth II and the younger daughter of King George VI and Queen Elizabeth .