Princess Elizabeth, heiress presumptive to the throne, pictured in the White Drawing Room at Buckingham Palace with her husband to be, Lieut. Philip Mountbatten and her sister Princess Margaret.
A young Princess Elizabeth at Buckingham Palace with her husband to be, Lieut Philip Mountbatten, and her sister, Princess Margaret. PA Images

The story of Lilibet: what the Queen's family nickname means and how it stuck