The country is witnessing something today it's never seen before in its history.
A Sapphire Jubilee.
In the early hours of 6 February 1952, King George VI passed away in his sleep - and although she didn't know it at the time (she was in Kenya with Prince Philip) his daughter Princess Elizabeth became Queen Elizabeth II.
Whilst the UK had witnessed a Diamond Jubilee before Queen Elizabeth's in 2012 (her great, great grandmother Queen Victoria celebrated hers in 1897) no British monarch has ever before reigned for 65 years.
The Queen always spends Accession Day at Sandringham. As for her, it's a sombre moment in which she reflects on her father's death.