The 21st birthday of Princess Elizabeth, on 21 April 1947, fell during the South African Tour undertaken by her parents King George VI and Queen Elizabeth, from February to April in that year.
The necklace, a gift from the Government of the Union of South Africa, was presented to the Princess by the South African Prime Minister, Field-Marshal Jan Smuts at the culmination of a ball held in Government House, Cape Town.
It originally consisted of a long chain of 21 graduated brilliants, the largest of 10 carats, each linked by a baguette-cut diamond and two small brilliant-cut diamonds.
The detachable snap-piece of the necklace was added later, using a 6-carat stone given to the Princess by Sir Ernest Oppenheimer, Chairman of De Beers, when the Princess visited the Big Hole Mine at Kimberley with her parents on 18 April 1947.
In 1952, the necklace was shortened to 15 large stones, and a bracelet was made from the six stones that were removed, together with the detachable snap-piece.