The Queen has said she wants Camilla, the Duchess of Cornwall, to be known as Queen Consort when Prince Charles becomes King.
In a message marking the 70th anniversary of her reign, the Queen said it was her “sincere wish” that Camilla would have that title.
The Queen is the first British monarch to celebrate a Platinum Jubilee.
She is spending her day privately on the Sandringham estate, with national celebrations to be held in June.
The Queen’s reign began when she was 25 years old, following the death of her father, George VI, on 6 February 1952.
The monarch said that, 70 years on, the day is one she remembers “as much for the death of my father, King George VI, as for the start of my reign”.
The Jubilee is the monarch’s first without the Duke of Edinburgh, her husband of 73 years, who died last year.
She reflected on how much she had gained from support given “unselfishly” by Prince Philip and thanked the goodwill shown to her by “all nationalities, faiths and ages in this country”.
During her reign, she has seen 14 British prime ministers occupy No 10.
Prime Minister Boris Johnson posted on Twitter: “I pay tribute to her many years of service and look forward to coming together as a country to celebrate her historic reign in the summer.”
Former prime ministers Theresa May and David Cameron also expressed their gratitude to the monarch.
Labour leader Sir Keir Starmer echoed these sentiments, saying he would like to express his “deepest thanks” for 70 years of “unparalleled public service”.
“Her Majesty The Queen has been one vital and valued constant in an ever-changing world, representing security and stability for our country, during the ups and downs of the last seven decades,” Sir Keir said.
The Women’s Institute (WI) posted several photos of the Queen over the years to social media, and congratulated her for 70 years of service. She is vice-president of the Sandringham WI.
The royal accession message, issued from her Sandringham estate in Norfolk, said the Queen still kept the promise of a lifetime of public duty, originally made in 1947 when she was 21, “that my life will always be devoted to your service”.
