Jubilee is a moment for contemplation

The Sapphire Jubilee is yet another milestone for the monarch

Longevity for a hereditary head of state has brought many milestones.

Britain's longest reigning monarch - she overtook her great great grandmother, Victoria, in 2015 - has already commemorated her Silver, Golden and Diamond Jubilees.

Today, after 23,742 days on the throne, it's the start of the first Sapphire Jubilee in British history.

For the Queen, it's a moment for contemplation rather than celebration - as it is also the anniversary of her father's death.

The woman who became Queen in 1952, when butter was still rationed in those post-war years, continues to reign, 65 years on, in a country now fashioning its future outside of the EU.

British photographer David Bailey took this portrait of the Queen, reissued for her Sapphire Jubilee

In the coming months and years, she will, inevitably, do less and other royals will take on more - most notably Prince William, once he finishes his job as an air ambulance pilot in the summer.

The 90-year-old working monarch has another significant moment on the horizon.

In November, she and Prince Philip will mark 70 years of marriage.