On Nov 20, 1947, the then Princess Elizabeth married Lt Philip Mountbatten, at London's Westminster Abbey.
Formerly Prince Philip of Greece and Denmark, he renounced his royal titles to become a naturalised British subject in order to marry Elizabeth, and was created Duke of Edinburgh before the wedding.
It is the second notable milestone of 2017 for the couple, now both in their nineties. On Feb 6 the Queen became the first British monarch to mark her Sapphire Jubilee - 65 years on the throne. She overtook her great-great-grandmother, Queen Victoria, to becoming the UK's longest-reigning monarch in Sep 2015.
Only four other monarchs are verifiably known to have passed the sapphire milestone.
King Sobhuza II of Swaziland, who led his country through independence until his death in 1982, reigned for 82 years - the longest verifiable reign of any monarch in recorded history.
King Bhumibol Adulyadej of Thailand had ruled for 70 years until his death in Oct 2016. He began his reign in 1946, aged 18.
Franz Joseph I, Emperor of Austria-Hungary, ruled for 67 years until his death in 1916. His nephew was Archduke Franz Ferdinand, whose assassination in 1914 sparked World War 1.
Louis XIV of France became king at the age of four on his father's death, and reigned for 72 years before his own death in 1715.
Date written/update: 2017-04-06