Buckingham Palace confirmed that the Queen and the Duke of Edinburgh will open the London Olympics in the summer.
A worldwide TV audience of over one billion people is expected to watch the royal couple open the Games at the 80,000-seater Olympic Stadium on July 27.
The Queen and Duke will also open the Paralympic Games at the same venue on August 29.
The Queen previously opened Canada's Montreal Games in 1976, while the Duke did it on her behalf at Melbourne, Australia, in 1956.
In 1948 - the last time the Olympics were held in the UK - King George VI opened the Games at Wembley Stadium.
And 40 years earlier his grandfather, King Edward VII, got proceedings under way at the first London Olympics at White City Stadium.
The 2012 opening ceremony's artistic director Danny Boyle said last month that it should make everyone feel like it is "the people's Games".
He said: "We would be very honoured if we are compared very favourably to Sydney (the 2000 Games) and this was another people's Games."
The sound of an enormous bell, set to be the biggest ringing bell in Europe, has been commissioned from a foundry in Whitechapel, east London, to kick off the proceedings.
Boyle has picked the title Isles of Wonder for his work on the ceremony, setting a target for himself to try to celebrate the best of British while representing all the regions.
This will be the first time the Queen has opened a Paralympic Games.
The 1984 Paralympic Games were officially opened by the Prince of Wales. These games were held in both Europe and North America, with the opening ceremony in Stoke Mandeville, Buckinghamshire - the birthplace of the Paralympic Games.
London 2012 chairman Lord Coe said: "This summer we will be hosting the largest Paralympic Games ever and the opening ceremony on August 29 will be a fantastic event.
"The Paralympic Games will undoubtedly be a time of extraordinary pride for our nation, and it is fitting that Her Majesty will declare us under way."
International Paralympic Committee president Sir Philip Craven said: "I am delighted that Her Majesty the Queen will be opening the Paralympic Games, further underlining the significance and status of these Games, not just to the Commonwealth but to the whole world."
