Image used for illustrative pruposes. Britain's Queen Elizabeth and her husband Prince Philip watch performers during a visit to the Manchester Central Convention Centre in Manchester, northern England March 23, 2012. The Queen is travelling around Britain to celebrate her Diamond Jubilee.

Britain's Queen Elizabeth and Prince Philip wait to greet guests prior to a state banquet at Bellevue presidential palace in Berlin, Germany June 24, 2015. Queen Elizabeth and the Duke of Edinburgh are on a three day state visit to Germany.

Britain's Queen Elizabeth watches as Prince Philip feeds an elephant during a visit to Whipsnade Zoo where the Queen opened the new Centre for Elephant Care, in Dunstable, Britain April 11, 2017.

Britain's Queen Elizabeth and Prince Philip laugh after bidding farewell to the President of Ireland Michael D. Higgins and his wife Sabina at Windsor Castle in Windsor, southern England April 11, 2014. The Irish President and his wife Sabina left Windsor at the end of a four day State Visit to Britain, during which they stayed at Windsor Castle as guests of Queen Elizabeth.

Britain's Queen Elizabeth addresses both Houses of Parliament, next to her husband Prince Philip at Westminster Hall in London March 20, 2012.

A pigeon flies ahead of Britain's Queen Elizabeth and Prince Philip, and Princes William, Harry and Kate Duchess of Cambridge behind as they wave to guests attending the Patron's Lunch on the Mall, an event to mark her 90th birthday, in London, June 12, 2016.

Britain's Queen Elizabeth is accompanied by Prince Philip as they proceed through the Royal Gallery before the State Opening of Parliament in the House of Lords, at the Palace of Westminster in London Britain May 27, 2015.

Britain's Queen Elizabeth II and the Duke of Edinburgh view the restored bed-chamber at the Maritime Museum in London, in this May 1, 1990 file photo. The Queen reopened the Queen's house at the Museum which has recently been refurbished at a cost of five million pounds sterling.

The hand of Britain's Queen Elizabeth II (L) is held by her husband, Prince Philip, Duke of Edinburgh, after her speech at the State Opening of Parliament in the House of Lords in London, November 13, 2002. Plans for a crackdown on crime and anti-social behaviour were at the heart of the Queen's Speech on November 13, which also included controversial plans for hospitals, jury trials and licensing laws.

Britain's Queen Elizabeth travels with Prince Philip on the new Scottish Borders railway line, in Scotland, September 9, 2015. Queen Elizabeth officialy opened the new Scottish Borders Railway on the day she became Britain's longest reigning monarch.

Queen Elizabeth II and Prince Philip share a moment as they attend the Beating the Retreat ceremony on Horseguards Parade, June 12, 1996. REUTERS/Stringer

Britain's Queen Elizabeth sits with Prince Philip as she delivers her speech in the House of Lords, during the State Opening of Parliament at the Palace of Westminster in London June 4, 2014. Reuters/Carl Court

Britain's Queen Elizabeth presents her husband Prince Philip with New Zealand's highest honour, the Order of New Zealand at Buckingham Palace in London June 6, 2013. Prince Philip celebrates his 92nd birthday on June 10.

Britain's Queen Elizabeth and Prince Philip, the Duke of Edinburgh walk at Broadlands in Romsey, southern England in this undated photograph taken in 2007. The Queen and Prince Philip will mark their diamond wedding anniversary with a special service of thanksgiving on November 19, 2007.

Britain's Queen Elizabeth and her husband Prince Philip pause during a tour of the Royal London Hospital in east London on February 27, 2013. The Queen opened the revamped hospital on Wednesday.