On her 21st birthday, she made her now famous radio broadcast from Cape Town in South Africa in 1947 on her first official overseas visit, declaring: "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."

With Philip stepping down from public duties, the Queen will increasingly turn to younger members of Team Windsor - namely the Prince of Wales and the Duke of Cambridge - to support her in her role.

William's job as an air ambulance pilot ends in the summer - neatly timed for him to become a full-time royal just before his grandfather retires.

The Queen no longer carries out overseas duties and, although she still holds investitures, a number are also carried out by Charles, William and the Princess Royal.

Buckingham Palace confirmed: "Her Majesty will continue to carry out a full programme of official engagements with the support of members of the Royal Family."

Philip, however, may pop up at public events from time to time.

He could choose to make appearances on the Palace balcony for Trooping the Colour in future years or even turn up to greet US President Donald Trump during his proposed State Visit.

In 1992, the Queen dismissed any speculation that she would step down, insisting frankly: "It is a job for life."

She was speaking about the death of her father, King George VI, for a BBC TV documentary, Elizabeth R, marking the 40th anniversary of her accession.

"In a way I didn't have an apprenticeship. My father died much too young and so it was all very sudden ... taking on and making the best job you can," the Queen said.

"It's a question of maturing into something that one's got used to doing, and accepting the fact that it's your fate, because I think continuity is very important. It is a job for life."