Britain's Queen Elizabeth leaves the Houses of Parliament in London after the State opening of Parliament ceremony, November 6, 2007. She is expected to become the longest serving British monarch on 9 September. REUTERS/Toby Melville

Seen here in full regalia for the State Opening of Parliament in London, May 9, 2012. She will pass the record set by her great-great-grandmother Queen Victoria with more than 63 years on the throne. REUTERS/Suzanne Plunkett

She will pass the record set by her great-great-grandmother Queen Victoria with more than 63 years on the throne. Seen here in full regalia at the State Opening of Parliament, at the Palace of Westminster, London May 8, 2013. REUTERS/Dan Kitwood/Pool

She is pictured walking through a field of ceramic poppies for the World War One centenary at the Tower of London, October 16, 2014. REUTERS/Luke MacGregor

Walking through the Royal Gallery after delivering her speech during the State Opening of Parliament in London, November 18, 2009. REUTERS/Carl De Souza/Pool

Known for her love of corgis, she smiles at one during a visit to Battersea Dogs & Cats Home in London, March 17, 2015. REUTERS/Ben Stansall/Pool

She pats Grand National favourite Teaforthree, during her visit to Cotts Equine Hospital in Narberth, Wales, April 29, 2014. REUTERS/Rebecca Naden

Senior members of Britain's royal family stand on the balcony of Buckingham Palace in the annual Trooping of the Colour ceremony to celebrate the Queen's official birthday, June 13, 2015. REUTERS/Stefan Wermuth

The Queen laughs at Windsor Castle, April 11, 2014. REUTERS/Leon Neal/Pool

One of her ceremonial duties is delivering a speech in the House of Lords, during the State Opening of Parliament at the Palace of Westminster, London, June 4, 2014. REUTERS/Suzanne Plunkett

Keeping up to date with new technologies, she delivered her Christmas message in 2012 in 3D. Here she watches a preview wearing customised 3D glasses, studded with Swarovski crystals in the form of a "Q". REUTERS/John Stillwell/Pool

A relaxed Queen cheering on competitors in a sack race with Prince Philip and Prince Charles at the Braemar Gathering in Scotland, September 1, 2012. REUTERSRussell Cheyne

Celebrating with John Warren (front R), her racing adviser and bloodstock manager, as she watches her horse Estimate win the Gold Cup at Ascot, England, June 20, 2013. REUTERS/Darren Staples

Touring the Foreign and Commonwealth Office during a visit to mark her Diamond Jubilee, London, December 18, 2012. REUTERS/Alastair Grant/Pool

A relaxed moment with her granddaughter-in-law Catherine, Duchess of Cambridge as they watch part of a children's sports event during a visit to Vernon Park in Nottingham, June 13, 2012. REUTERS/Phil Noble

A stern-looking Queen alongside Prince Phillip and various dignitaries at the opening ceremony of the London 2012 Olympic Games, July 27, 2012. REUTERS/Kai Pfaffenbach

Known for her love of horses and racing, the Queen is pictured here smiling after the Derby horse race in Epsom, June 2, 2012. REUTERS/Toby Melville

Members of the Team GB Olympic Water Polo team tower over the Queen during a garden party held at Buckingham Palace, London, May 30, 2013. REUTERS/Pool/Jonathan Brady

Wearing a headscarf she attends a tree planting ceremony in the Diamond Jubilee Wood on her Sandringham Estate in Norfolk, England, February 3, 2012. REUTERS/Arthur Edwards/Pool

An intimate moment with her grandson Prince William, after being shown around a Sea King search and rescue helicopter during a visit to RAF Valley, Wales, April 1, 2011. REUTERS/Christopher Furlong/Pool

A sombre moment as she attends the annual Remembrance Sunday ceremony at the Cenotaph in Whitehall, London, November 14, 2010. REUTERS/Stefan Wermuth

A contemplative moment as she travels by train to Potsdam on a state visit to Germany, November 3, 2004. REUTERS/Ian Jones/Pool

Looking every inch the Queen as she leaves Buckingham Palace in a horse drawn carriage to attend the State Opening of Parliament, London, May 25, 2010. REUTERS/Suzanne Plunkett

The Queen leaves after attending a service of commemoration to mark the end of combat operations in Iraq, at St Paul's Cathedra, London, October 9, 2009. REUTERS/Luke MacGregor

A moment of intimacy between mother and son as Prince Charles kisses her hand, during a visit to the Chelsea Flower Show, London, May 18, 2009. REUTERS/Sang Tan/Pool

Arm in arm, the Queen and Prince Philip, the Duke of Edinburgh walk at Broadlands in Romsey, England in this undated photograph taken in 2007. REUTERS/Fiona Hanson/Pool

The Queen has met many VIP's during her reign including Lady Gaga in December 7, 2009. REUTERS/Leon Neal/Pool

Prince Philip looks out of a window as the Queen poses for a picture with Wanda Henton Brown, the wife of Bermuda Premier Ewart Brown, prior to a state dinner in Bermuda, November 25, 2009. REUTERS/Hans Deryk

Britain's Prime Minister David Cameron bows to his Queen, London, March 3, 2015. REUTERS/Toby Melville

Former Prime Ministers, the late Lady Thatcher (L) and Tony Blair and Blair's wife Cherie with the Queen, June 14, 2007. REUTERS/Stephen Hird (BRITAIN)

With former U.S. President George W. Bush and First Lady Laura Bush in London, November 21, 2003. REUTERS/Jason Reed

With President Vladimir Putin, London, June 24, 2003. REUTERS/Grigory Dukor

Smiling during a visit to the set of the television show Game of Thrones in the Titanic Quarter of Belfast, Northern Ireland, June 24, 2014. REUTERS/Phil Noble

The proud grandmother can't hide her smiles as Prince Harry lines up during the Sovereign's Parade at the Royal Military Academy in Sandhurst, April 12, 2006. REUTERS/Dylan Martinez

Riding her beloved horse in the grounds of Windsor
Castle just days after her mother died, April 2, 2002. REUTERS/Dan Chung

An introduction to the star of the theatre production of "War Horse", during a visit to the National Theatre, London October 22, 2013. REUTERS/Lefteris Pitarakis/Pool

Sheltering under umbrellas at the "Wild London" exhibition in Richmond, London May 15, 2012. REUTERS/Suzanne Plunkett

The Queen is not amused as her horse loses in the Epsom Derby alongside Prince Edward, June 4, 2011. REUTERS/Suzanne Plunkett

A wide smile during a visit to the Irish National Stud in Kildare, Ireland May 19, 2011. REUTERS/Dylan Martinez

Alongside Carole Middleton and Camilla, Duchess of Cornwall, after the wedding ceremony of Prince William and Kate Middleton at Westminster Abbey, London, April 29, 2011. REUTERS/Toby Melville

The Queen at Windsor Castle, October 26, 2010. REUTERS/Dan Kitwood/Pool

Waiting for a meeting with Liberal Leader Michael Ignatieff at Rideau Hall in Ottawa, Canada July 2, 2010. REUTERS/Blair Gable

Another light-hearted moment with Prince Harry at the wedding of Prince Charles and Camilla, Duchess of Cornwall at St. George's Chapel in Windsor Castle, April 9, 2005. REUTERS/Alastair Grant/Pool

Pointing and laughing with Prince Charles as they watch a sack race with Princess Anne (R) during the Braemar Gathering September 5, 2009. REUTERS/Russell Cheyne

The Queen proves not to be a fan of modern cooking techniques as she watches chef Heston Blumenthal makes ice cream using liquid nitrogen during the launch of the Royal Institution of Great Britain in London, May 28, 2008. REUTERS/Luke MacGregor (BRITAIN)

She is seen on a television screen making her speech next to a painting of herself as a young woman during the State Opening of Parliament in London, November 15, 2006. REUTERS/Luke MacGregor

Receiving a scroll from Bruce Two Dogs Bozsum at Southwark Cathedral in London, November 22, 2006. REUTERS/Stefan Rousseau/Pool

A very glamorous-looking Queen arrives for the world premiere of the James Bond movie "Casino Royale", London, November 14, 2006. REUTERS/Alessia Pierdomenico

And in contrast she boarded a train at Kings Cross station en route to Kings Lynn in Norfolk, December 17, 2009. REUTERS/Stefan Rousseau/Pool

Eyeing up a pint of Guinness at the Guinness Storehouse, in Dublin, May 18, 2011. REUTERS/Tony Maxwell /Pool

Having fun with Prince William watching the annual Braemar Gathering in the Grampian Highlands of Scotland, September 3, 2005. REUTERS/Robert Paterson

Showing her sense of humour as she is caught laughing when a swarm of bees delayed proceedings during her review of the Grenadier Guards on the lawn of Windsor Castle, April 15, 2003. REUTERS/Chris Young/Pool

She looks out from her horse drawn carriage as she is driven to the Palace of Westminster in London, May 17, 2005. REUTERS/Dylan Martinez

Leaving a Christmas Day service at St Mary Magdalene Church on the Royal estate at Sandringham, December 25, 2010. REUTERS/Toby Melville

Wearing the State Crown during State Opening of Parliament in London, November 23, 2004. REUTERS/Russell Boyce

White clothes, white fur and a silver handbag following the State Opening of Parliament, London, December 3, 2008. REUTERS/Toby Melville

An emotional Queen leaves St Paul's Cathedral after a
memorial service for the victims 9/11 with American Ambassador William Farish, London, September 14, 2001. REUTERS/Ferran Paredes

A poignant moment as the Queen, and a visibly distressed Prince Charles, walk behind the Queen Mother's coffin
following her funeral at Westminster Abbey in central London, April 9, 2002. REUTERS/Dan Chung

In mourning, as she leaves Westminster Abbey by car following the funeral of her mother in central London, April 9, 2002. REUTERS/Ian Waldie

Surrounded by flowers laid outside Buckingham Palace after the death of Diana, Princess of Wales, September 5, 1997. REUTERS/Ian Waldie