TODAY MARKS QUEEN Elizabeth II’s 90th birthday.

The monarch has reigned for 64 years, during which time the British empire has changed dramatically.

There have been 12 prime ministers over the course of her reign.

The Duke and Duchess of York with their baby daughter Princess Elizabeth on 29 April 1926. PA Archive / Press Association Images PA Archive / Press Association Images / Press Association Images

Elizabeth Alexandra Mary Windsor, known as Lilibet, was born on 21 April 1926, with no expectation of being queen.

Her fate dramatically changed when her childless uncle Edward VIII abdicated in 1936 to marry Wallis Simpson, a twice-divorced American.

Princess Elizabeth arriving at the 16th Century Church at Balcombe, Sussex, for the wedding of Lady May Cambridge and Captain Henry Abel Smith on 24 October 1931. PA Archive / Press Association Images PA Archive / Press Association Images / Press Association Images

Princess Elizabeth’s father inherited the crown as George VI and she suddenly became heir to the throne.

On her 21st birthday, she vowed to spend her life serving her country, but this promise was put to the test sooner than she could have imagined.

Her father died suddenly in 1952 at the age of 56, making Elizabeth queen at the age of 25.

The scene after the crowning ceremony on 2 June 1953 in Westminster Abbey, showing the Queen wearing the St Edward Crown and carrying the Sceptre and the Rod. orla orla

She was by then married to Philip, a distant cousin, whom she has described as “my strength and stay”.

They have four children: Charles (born in 1948) Anne (1950), Andrew (1960) and Edward (1964).

Here are photos from each of the six decades she has reigned in: