William and Kate throughout the years

June 15, 1985: Prince William makes a royal salute as he watches the scene of Trooping the Colour from the balcony of Buckingham Palace with his brother Harry and mother Princess Diana in London. (Reuters)  

Aug. 9, 1988: Princess Diana tries to get her son, Prince Harry, to smile for the cameras while his brother Prince William squints from the bright sun. (Reuters) 

Oct. 1990: Diana, Princess of Wales is seen arriving at a memorial service with her sons William and Harry during the 50th anniversary of the Blitz of London. (Reuters)

Sept. 6, 1995: The Prince and Princess of Wales, Prince Harry, and housemaster Dr Andrew Gayley escort Prince William, second in line to the throne, for his first day of term at the world famous Eton College. (Reuters) 

March 9, 1997: Members of the British Royal Family sit for an official portrait in the white drawing room at Windsor Castle after Prince William's confirmation at St Georges Chapel. Pictured are, (Left to Right Front Row) Prince Harry, Diana Princess of Wales, Prince William, the Prince of Wales, Queen Elizabeth, (back row Left to Right) King Constatine of Greece, Lady Susan Hussey, Princess Alexandra, the Duchess of Westminster, and Lord Romsey. (Reuters) 

Sept. 6, 1997: Prince Charles with his two sons Prince Harry and Prince William and Diana's brother Earl Spencer bow their heads as they watch the hearse bearing the coffin of Diana, Princess of Wales leave Westminster Abbey. (Reuters)

2005: This image shows Britain's Prince William and Kate Middleton together following their graduation from St. Andrews University, Scotland. (AP/The Middleton Family)

June 23, 2005: Britain's Prince William's then-girlfriend Kate Middleton leaves after attending their university graduation ceremony at St. Andrews University in St. Andrews, Scotland. (AP)

Feb. 10, 2007: Britain's Prince William and his then-girlfriend Kate Middleton watch the England vs. Italy Six Nations international rugby union match at Twickenham in London. (Reuters) (Reuters)

Nov. 16, 2010: Britain's Prince William and his then-fiancee Kate Middleton pose for a photograph in St. James's Palace, central London. (Reuters) (Reuters)

Dec. 18, 2010: Britain's Prince William and his then-fiancee Kate Middleton arrive at The Thursford Collection in Norfolk, England. (Reuters)

April 29, 2011: Britain's Prince William and his bride Catherine, Duchess of Cambridge, pose for an official photograph, with their bridesmaids and pageboys, on the day of their wedding at Buckingham Palace. (Reuters) (Reuters)

April 29, 2011: Britain's Prince William and his wife Catherine, Duchess of Cambridge kiss on the balcony of Buckingham Palace, following following their wedding at Westminster Abbey in London. (Reuters) 

April 29, 2011: Britain's Prince William and Catherine, Duchess of Cambridge, look at one another after their wedding ceremony in Westminster Abbey, in central London. (Reuters) (Reuters)

Dec. 21, 2011: Britain's Prince William dances with Vanessa Boateng as his wife Catherine,  Duchess of Cambridge looks on during a reception at Centrepoint's Camberwell Foyer in London. (Reuters)

Dec. 25, 2011: Britain's Prince William, Prince Charles and Catherine, Duchess of Cambridge arrive for a Christmas Day service at St Mary Magdalene Church in east England. (Reuters) (Reuters)

June 13, 2012: Britain's Catherine, Duchess of Cambridge, is given flowers by Brendon Morris during a visit to Market Square, Nottingham. (Reuters)

July 26, 2012: Britain's Catherine, Duchess of Cambridge controls a ball next to Prince William during a visit to Bacon's college to launch the Coach core sports programme, which is a partnership between the Royal Foundation of The Duke and Duchess of Cambridge and Greenhouse charity, a day before the London 2012 Olympics opening ceremony in Rotherhithe. (Reuters) 

Aug. 30, 2012: Britain's Prince William and Catherine, Duchess of Cambridge take part in a wave during the London 2012 Paralympic Games. (Reuters)  (Reuters)

Dec. 6, 2012: Britain's Prince William stands next to his wife Kate, Duchess of Cambridge as she leaves the King Edward VII hospital in central London. (AP) (AP)

April 26, 2013: Britain's Prince Harry, Catherine, Duchess of Cambridge and her husband Prince William raise their wands on the set used to depict Diagon Alley in the Harry Potter films, during the inauguration of Warner Bros. Studios Leavesden in London. (Reuters) (Reuters)