Queen Elizabeth II becomes Britain’s longest-reigning monarch later when she passes the record set by her great-great-grandmother Queen Victoria, teh BBC reports.
The Queen will have reigned for 63 years and seven months – calculated at 23,226 days, 16 hours and approximately 30 minutes at about 17:30 BST.
Prime Minister David Cameron will lead tributes in the House of Commons and there will be a River Thames salute.
Business in the Commons will be postponed for half an hour so MPs can pay tribute to the Queen.
Buckingham Palace has released an official photograph to mark the occasion, taken by Mary McCartney in the Queen’s private audience room.
This is where she holds weekly audiences with prime ministers of the day, and receives visiting heads of state and government.
