Quiz: Queen Elizabeth ll - 63 years on the throne

Elizabeth became Queen unexpectedly early on February 6, 1952 when she was 25 and was crowned on June 2, the following year. The fulfilment of a promise had begun.

On her 21st birthday when she was in South Africa with her parents and younger sister Margaret, an earnest Princess Elizabeth made a long and moving speech which ended: "I declare before you all that my whole life whether it be long or short shall be devoted to your service and the service of our great imperial family to which we all belong.

"But I shall not have strength to carry out this resolution alone unless you join in it with me, as I now invite you to do.

"I know that your support will be unfailingly given. God help me to make good my vow, and God bless all of you who are willing to share in it."

Never once has the Queen betrayed that pledge.

Fast forward just a few short years to a balmy February in Kenya. Princess Elizabeth had been out with her own camera picturing that lovely land.

She and her husband Prince Philip were staying at the famous Tree Tops hotel and enjoying seeing Kenya as well as representing her father, King George VI who only days before had waved them off at a foggy London airport.

But now, the clouds were gathering at home. The King, Elizabeth's beloved papa, had died in his sleep.

She was the Queen.

Today, we and she along with millions across the globe unite to mark what has become the longest reign.

The Coronation was delayed for 16 months, partly because it was felt that such a celebration was not appropriate during the long period of mourning after a sovereign's death.

The Queen has never thought that celebrating this moment was in order.

But she does have a special dinner tonight after an important appointment opening the United Kingdom's biggest new domestic railway line for more than a century in that land she loves so much – Scotland.

Maybe with a hint of Victorian charm, the Queen agreed to travel by steam train from Edinburgh to Tweedbank near Galashiels to formally open the new Borders Railway and re-live a rail tradition which began back in the 1840s when great-great grandma Victoria was Queen.

But however Her Majesty wanted to spend today, she will surely reflect – perhaps quietly and privately – back to June 1953 when the formal recognition, the pomp and the ceremony marked the beginning of the rest of her life. A new reign had started and now, it becomes the longest in our history.

The Queen has embraced all the momentous changes and is still a steadfast rock for family, nation and Commonwealth.

Her Majesty truly has been and remains a treasure.