Prince Philip leaves after a service of thanksgiving for Queen Elizabeth's 90th birthday at St Paul's Cathedral in London, Britain, June 10, 2016. REUTERS/Ben Stansall/Pool 

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. REUTERS/Leon Neal/Pool 

Queen Elizabeth addresses both Houses of Parliament, next to Prince Philip at Westminster Hall in London March 20, 2012. REUTERS/Jack Hill/Pool 

The hand of Queen Elizabeth is held by Prince Philip after her speech at the State Opening of Parliament in the House of Lords in London, November 13, 2002. REUTERS/Russell Boyce 

The Queen Elizabeth II, Prince Philip and David Webster speak with ballerina Margot Fonteyn at CG Gala June 10, 1958. REUTERS/Stringer BEST QUALITY AVAILABLE 

Queen Elizabeth and Prince Philip view the restored bed-chamber at the Maritime Museum in London, May 1, 1990. REUTERS/Mike Parsson 

Prince Philip, in his role as the Regiment Colonel in Chief, visits The Queens Royal Hussars in Basra, Iraq, October 2006. REUTERS/Ministry of Defence 

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. REUTERS/Suzanne Plunkett 

A pigeon flies ahead of Queen Elizabeth and Prince Philip, and Princes William, Harry and Catherine, 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. REUTERS/Toby Melville 

Queen Elizabeth and Prince Philip wait to greet guests prior to a state banquet at Bellevue presidential palace in Berlin, Germany June 24, 2015. REUTERS/Wolfgang Kumm/Pool 

Queen Elizabeth, Prince Philip and Prince Charles watch the sack race at the annual Braemar Highland Gathering in Braemar, Scotland, Britain September 5, 2015. REUTERS/Russell Cheyne 

Prince Philip meets Ian "Spike" Betterton, Chair of The Friends of St Georges Park, during a visit to Kidderminster in central England July 11, 2012. REUTERS/Heathcliffe O'Malley/Pool 

Queen Elizabeth talks with her grandson Prince William, watched by Prince Philip, after being shown around a Sea King search and rescue helicopter during a visit to RAF Valley, in north Wales April 1, 2011. Prince William was serving as a search and rescue helicopter pilot, based at RAF Valley on Anglesey, an island off the north west coast of Wales. REUTERS/Christopher Furlong/Pool 

Prince Philip smiles after presenting Royal Medals at the Royal Society of Edinburgh, in Edinburgh August 12, 2013. REUTERS/Andrew Milligan/Pool 

Queen Elizabeth leaves with Prince Philip after a service of thanksgiving for her 90th birthday at St Paul's Cathedral in London, Britain, June 10, 2016. REUTERS/Peter Nicholls 

Queen Elizabeth, Prince Philip and Prince William walk amongst spring blossom and flowers in Windsor, southern England March 31, 2014. REUTERS/Toby Melville 

Queen Elizabeth travels with Prince Philip on the new Scottish Borders railway line, in Scotland, September 9, 2015. REUTERS/Andrew Milligan/Pool 

Members of the royal family, including Prince Charles, Catherine, Duchess of Cambridge holding Princess Charlotte, Prince George, Prince William, Queen Elizabeth, and Prince Philip watch a flypast as they stand on the balcony of Buckingham Palace after the annual Trooping the Colour ceremony on Horseguards Parade in central London, Britain June 11, 2016. REUTERS/Toby Melville 

Britain's Prince Philip (L) leaves after presenting Royal Medals at the Royal Society of Edinburgh, in Edinburgh August 12, 2013. The Prince, making his first public appearance since his hospital admission in June, presented the Royal Medals which are awarded for a range of subjects. REUTERS/Andrew Milligan/Pool (BRITAIN - Tags: ENTERTAINMENT EDUCATION SOCIETY ROYALS) 

Britain's Prince Charles (2nd L) greets his father Prince Philip, watched by his wife, Camilla, Duchess of Cornwall (R) and his son Prince Harry (3rd R), during a visit to Prince Harry's Sentebale 'Forget-Me-Not' garden, representing his Sentebale charity, at the Chelsea Flower Show in central London May 20, 2013. The annual show opens to the public on Tuesday. REUTERS/Geoff Pugh/Pool (BRITAIN - Tags: ENTERTAINMENT ENVIRONMENT SOCIETY ROYALS) 

His Royal Highness Prince Philip, Duke of Edinburgh entrusts new regimental colours to Lieutenant Bronson Peacock from 3rd Battalion of The Royal Canadian Regiment at a Queen's Park ceremony in Toronto April 27, 2013. The Duke of Edinburgh has been the Colonel-in Chief of the Royal Canadian Regiment since 1953. REUTERS/Fred Thornhill (CANADA - Tags: ENTERTAINMENT MILITARY POLITICS ROYALS TPX IMAGES OF THE DAY) 

Britain's Queen Elizabeth waits to read the Queen's Speech to lawmakers in the House of Lords, next to Prince Philip, during the State Opening of Parliament in central London May 9, 2012. REUTERS/Oli Scarff/POOL (BRITAIN - Tags: ENTERTAINMENT POLITICS SOCIETY ROYALS) 

Britain's Queen Elizabeth and Prince Philip arrive for the fourth day of racing at Royal Ascot in southern England June 18, 2010. REUTERS/Stefan Wermuth (BRITAIN - Tags: SPORT ROYALS HORSE RACING SOCIETY) 

Britain's Duke of Edinburgh attends the Colonel's Review ceremony at Horse Guards Parade in London, June 5, 2004. The annual military parade and march-past by the British Army Household Division takes place a week before the Trooping of the Colour which marks Queen Elizabeth's official birthday. REUTERS/Toby Melville (BRITAIN - Tags: SOCIETY ROYALS) 

Britain's Queen Elizabeth (C) and Wanda Henton Brown, the wife of Bermuda Premier Ewart Brown, wait for the beginning of the receiving line as Prince Philip (L) looks out of a window prior to a state dinner in Bermuda November 25, 2009. The Queen's three-day visit is in conjunction with the 400th anniversary of settlement on the island. REUTERS/Hans Deryk (BERMUDA POLITICS ROYALS ANNIVERSARY) 

Britain's Queen Elizabeth II (R) and her husband Prince Philip (L) watch as an orphan performs at the Mildmay HIV Centre in Kampala, Uganda November 22, 2007, on the first day of her state visit to Uganda. The Queen is due to officiate at the opening of the Commonwealth Heads of Government Meeting (CHOGM) November 22, 2007.REUTERS/Jon Hrusa/Pool (UGANDA) 

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. REUTERS/Fiona Hanson/Pool (UNITED KINGDOM) 

Britain's Duke of Edinburgh samples a glass of 'Jubilee ale' at the
Bass Museum in Burton upon Trent in Staffordshire July 3, 2002. Prince
Philip, along with his wife Britain's Queen Elizabeth II, visited the
area on the second day of their Golden Jubilee tour of the West
Midlands. REUTERS/Michael Dunlea/POOL

NMB 

Britain's Duke of Edinburgh listens to local people during a garden
party at Hillsborough Castle, County Down in Northern Ireland July 30,
2001. Prince Philip is visiting in conjunction with The Duke of
Edinburgh Award scheme.

PM/NMB 

Britain's Queen Elizabeth II and Prince Phillip, the Duke of Edinburgh, wearing their Order of the Garter robes, ride in an open-topped carriage to Windsor Castle following the Garter Ceremony, June 18, 2001. The ceremony is held annually to formally install the New Knights of the Garter. 

Queen Elizabeth II and Prince Philip attend the Beating the Retreat ceremony on Horseguards Parade, June 13. The Retreat, which was played by the massed bands of the Royal Marines, was in honour of Prince Philip's 75th birthday, Philip is the Captain General of the Royal Marines. 

Britain's Prince Philip pauses in front of a life-sized cartoon of himself at the opening of New Zealand cartoonist Sir David Low's, exhibition at the National Library in Wellington, November 7. [Lowe, who died in 1963 and who's work was syndicated worldwide drew the picture of Prince Philip in 1953 after the coronation of his wife, Queen-Elizabeth II].
**NEW ZEALAND OUT 

Britain's Prince Philip looks at a display before presenting Royal Medals at the Royal Society of Edinburgh, in Edinburgh August 12, 2013. The Prince, making his first public appearance since his hospital admission in June, presented the Royal Medals which are awarded for a range of subjects. REUTERS/Andrew Milligan/Pool (BRITAIN - Tags: ENTERTAINMENT EDUCATION SOCIETY ROYALS) 

A man arrives with birthday balloons and flowers at the London Clinic in London June 10, 2013. Britain's Prince Philip is recovering after an operation at the hospital and celebrates his 92nd birthday today. REUTERS/Luke MacGregor (BRITAIN - Tags: ROYALS ENTERTAINMENT) 

Britain's Prince Philip arrives on the eve of his 90th birthday to take the salute of the Household Division Beating Retreat on Horse Guards Parade in London June 9, 2011. REUTERS/Paul Edwards/Pool (BRITAIN - Tags: ROYALS HEADSHOT) 

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. REUTERS/Anthony Devlin/POOL (BRITAIN - Tags: ROYALS ENTERTAINMENT POLITICS) 

Britain's Prince Philip waves to members of the media as he leaves the King Edward VII Hospital in London June 9, 2012. The husband of Britain's Queen Elizabeth left hospital on the eve of his 91st birthday on Saturday, five days after he was taken ill during celebrations to mark the monarch's 60 years on the throne. REUTERS/Paul Hackett (BRITAIN - Tags: ROYALS ENTERTAINMENT SOCIETY) 

Britain's Prince Philip officially opens the "Tiger Territory" enclosure at London Zoo March 20, 2013. The 2,500 square meter enclosure which cost £3.6 million GBP (U.S. $5.44 million) houses Jae Jae, a male Sumatran tiger, and Melati, a female Sumatran tiger. REUTERS/Leon Neal/pool (BRITAIN - Tags: ANIMALS ROYALS ENTERTAINMENT SOCIETY) 

Britain's Queen Elizabeth and Prince Philip attend a service celebrating the 60th anniversary of the Queen's coronation at Westminster Abbey in London June 4, 2013. Britain's Queen Elizabeth returned to the scene of her coronation on Tuesday to mark a reign that has weathered six decades of social transformation and the end of her country's global empire. REUTERS/Jack Hill/Pool (BRITAIN - Tags: ANNIVERSARY ENTERTAINMENT SOCIETY ROYALS) 

Britain's Queen Elizabeth (L) and Prince Philip (R) leave after the State Opening of Parliament, at the Palace of Westminster in London May 8, 2013. REUTERS/Kirsty Wigglesworth/Pool (BRITAIN - Tags: ENTERTAINMENT POLITICS SOCIETY ROYALS) 

Britain's Prince Philip, Duke of Edinburgh attends the Epsom Derby in Epsom, south of London, June 1, 2013. REUTERS/Andrew Winning (BRITAIN - Tags: SPORT HORSE RACING SOCIETY ENTERTAINMENT ROYALS) 

Britain's Prince Philip takes part in a ceremonial welcome for United Arab Emirates President Sheikh Khalifa bin Zayed bin Sultan Al Nahyan during his state visit at Windsor Castle, in Windsor, southern England April 30, 2013. REUTERS/Toby Melville (REUTERS - Tags: ENTERTAINMENT POLITICS SOCIETY ROYALS) 

Britain's Prince Philip the husband of Queen Elizabeth, leaves after the Commonwealth Day Observance service at Westminster Abbey in central London March 11, 2013. The Queen, who is the head of the Commonwealth, pulled out of attending the service as she continues to recover from a recent illness. REUTERS/Matt Dunham/Pool (BRITAIN - Tags: POLITICS SOCIETY RELIGION ROYALS) 

Britain's Prince Philip waits for the arrival of the Emir of Kuwait, Sheikh Sabah al-Ahmad al-Sabah, at Windsor Castle at the start of his state visit, in Windsor, in southern England November 27, 2012. REUTERS/Alastair Grant/Pool (BRITAIN - Tags: ENTERTAINMENT POLITICS SOCIETY ROYALS) 

Britain's Prince Philip attends a service at the Field of Remembrance at Westminster Abbey in London November 8, 2012. REUTERS/Olivia Harris (BRITAIN - Tags: ROYALS MILITARY ANNIVERSARY) 

Britain's Prince Philip officially opens the new Cellarium Cafe at Westminster Abbey in central London October 17, 2012 . REUTERS/Oli Scarff/Pool (BRITAIN - Tags: ROYALS ENTERTAINMENT SOCIETY RELIGION) 

Britain's Prince Philip visits the Aquatics Centre with Princess Anne in London July 28, 2012. REUTERS/Neil Hall (BRITAIN - Tags: SPORT OLYMPICS ROYALS) 

Britain's Queen Elizabeth and Prince Philip, Duke of Edinburgh, arrive to attend the fifth day of racing at the Royal Ascot, southwest of London June 23, 2012. REUTERS/Stefan Wermuth (BRITAIN - Tags: SPORT HORSE RACING ROYALS ENTERTAINMENT) 

Britain's Queen Elizabeth receives the trophy from Prince Philip, Duke of Edinburgh, after her horse Estimate won The Queen's Vase on the fourth day at Royal Ascot, southwest of London June 22, 2012. REUTERS/Stefan Wermuth (BRITAIN - Tags: SPORT HORSE RACING SOCIETY ROYALS ENTERTAINMENT) 

Britain's Prince Philip and Princess Anne attend the equestrian Eventing Individual Dressage Day 2 in the Greenwich Park during the London 2012 Olympic Games, July 29, 2012. REUTERS/Mike Hutchings (BRITAIN - Tags: ENTERTAINMENT SPORT EQUESTRIANISM OLYMPICS ROYALS)

Britain's Queen Elizabeth (L) and her husband Prince Philip watch from the forecourt of Buckingham Palace during the Trooping the Colour ceremony in central London June 16, 2012. Trooping the Colour is a ceremony to honour the sovereign's official birthday. REUTERS/Toby Melville (BRITAIN - Tags: ANNIVERSARY ENTERTAINMENT MILITARY SOCIETY ROYALS) 

Britain's Queen Elizabeth visits the ArcelorMittal Orbit tower with Prince Philip (R) in London July 28, 2012. REUTERS/Neil Hall (BRITAIN - Tags: SPORT OLYMPICS ROYALS) 

Britain's Queen Elizabeth (C) and Prince Philip (centre 2nd R) arrive at the opening ceremony as International Olympic Committee (IOC) President Jacques Rogge (centre 2nd L), wife of British Prime Minister David Cameron, Samantha Cameron (front 2nd R), and other members of the audience applaud at the London 2012 Olympic Games at the Olympic Stadium July 27, 2012. REUTERS/Mike Blake (BRITAIN - Tags: SPORT OLYMPICS ENTERTAINMENT ROYALS POLITICS)

Britain's Queen Elizabeth (R), Prince Philip (2nd R), and Olympic torch bearer Gina Macgregor (2nd L) watch as torchbearer Phil Wells takes the Olympic Flame at Windsor Castle, west of London July 10, 2012. REUTERS/Ben Stansall/Pool (BRITAIN - Tags: ROYALS SPORT OLYMPICS SOCIETY) 

Members of Britain's Royal family (L-R) Prince Charles, Prince Edward, Queen Elizabeth, Princess Anne, Prince Philip, Tim Lawrence, Louise Windsor, Catherine, Duchess of Cambridge and Prince William, watch a flypast by the Red Arrows as they stand on the balcony of Buckingham Palace following the Trooping the Colour ceremony in central London June 16, 2012. Trooping the Colour is a ceremony to honour the sovereign's official birthday. REUTERS/Toby Melville (BRITAIN - Tags: ANNIVERSARY ENTERTAINMENT MILITARY SOCIETY ROYALS) 

Britain's Queen Elizabeth arrives with Prince Philip (R) at the Diamond Jubilee Pageant in Windsor, Berkshire May 13, 2012. REUTERS/Jane Mingay/Pool (BRITAIN - Tags: POLITICS ROYALS ENTERTAINMENT) 

Britain's Queen Elizabeth and Prince Philip view the horses from the parade ring before the Diamond Jubilee Coronation Cup race at the Epsom Derby festival in Epsom, southwest of London June 2, 2012. Queen Elizabeth gets four days of celebrations to mark her 60 years on the British throne under way on Saturday with one of her favourite pastimes, a trip to the horse races, as tributes to the long-serving monarch pour in. REUTERS/Ben Stansall/pool (BRITAIN - Tags: ROYALS ENTERTAINMENT SPORT HORSE RACING SOCIETY) 

Britain's Queen Elizabeth (R) and Prince Philip, The Duke of Edinburgh, view horses in the parade ring at the Epsom Derby festival, part of the Queen's Diamond Jubilee celebrations, in Epsom, southwest of London June 2, 2012. Queen Elizabeth gets four days of celebrations to mark her 60 years on the British throne under way on Saturday with one of her favourite pastimes, a trip to the horse races, as tributes to the long-serving monarch pour in. REUTERS/Toby Melville (BRITAIN - Tags: SPORT HORSE RACING ROYALS) 

Britain's Prince Philip (C) talks to Prince Charles (L), Prince William (2nd R) and Prince Harry on the Spirit of Chartwell during the Diamond Jubilee River Pageant on the River Thames, in London June 3, 2012. Queen Elizabeth joined an armada of 1,000 boats in a gilded royal barge, in a pageant down the River Thames on Sunday in a spectacular highlight of four days of nationwide celebrations to mark her Diamond Jubilee. REUTERS/John Stillwell/Pool (BRITAIN - Tags: ROYALS ENTERTAINMENT SOCIETY ANNIVERSARY) 

Britain's Queen Elizabeth (L) and Prince Philip visit Burnley College and University of Central Lancashire in northern England May 16, 2012. The Queen and the Prince are on a two-day visit to northwest England. REUTERS/Paul Grover/Pool (BRITAIN - Tags: ROYALS ENTERTAINMENT SOCIETY)