The 95-year-old is the longest-reigning monarch in British history and is set to celebrate 70 years on the throne next June. The Queen ascended to the throne in 1952, but five years earlier during a tour of South Africa, she made a commitment to dedicate her entire life to the service of the Commonwealth.

       Speaking on her 21st birthday on April 21, 1947, the then Princess Elizabeth said: “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.”

       Princess Elizabeth made the commitment without envisaging she would become the longest-reigning monarch.

       Mr Harrold, who served in the royal household from 2004-2011, added the Queen would never consider abdicating and would only think of passing on more royal duties.

       He added: “I do not believe the Queen would ever enter into any negotiations about stepping down as our Queen.

       “I can however see her reducing her workload which is not unreasonable for a 95-year-old and passing more of them onto the younger royals.”

       The Queen became the UK's longest-serving monarch on September 9, 2015.

       DON'T MISS

       Prince William and Charles facing 'element of competition' [INSIGHT]

       Queen talks to her two callers through an "anti-hacked" phone [VIDEO]

       UK snow warning: The exact time snow could fall this weekend [FORECAST]

       She surpassed the 63 years, seven months and two day-long reign of her great-great-grandmother Queen Victoria.

       The Prince of Wales became the longest-serving heir in 2011.

       Prince Charles broke the previous record of 59 years, two months and 13 days, set by his great-great-grandfather, King Edward VII.

       The Queen’s uncle, King Edward VIII, is the only monarch in British history to abdicate.

       He stepped aside in 1936 in order to marry American socialite Wallis Simpson, as she was a divorcée, he was not allowed to marry her otherwise.

       The Queen’s Platinum Jubilee celebrations will take place during a four-day bank holiday weekend from June 2, 2022.

       A Trooping of the Colour parade, a royal trip to the Derby at Epsom Downs and a live concert outside Buckingham Palace are some the events lined-up to mark the historical occasion.