See Prince William and Kate Middleton's Sweetest Moments

Prince William and Kate Middleton pose for photographs in the State Apartments of St James Palace after announcing their engagement. The couple became engaged during a recent holiday in Kenya having been together for eight years. London, Nov. 16, 2010.

Prince William and Catherine kiss on the balcony of Buckingham Palace after getting married in London on April 29, 2011.

Catherine and Prince William during Day 6 of the London 2012 Olympic Games on Aug. 2, 2012.

Prince William and Catherine with their newborn son, Prince George, depart the Lindo Wing of St Mary's Hospital in London on July 23, 2013.

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge hold puppies during a visit to the Royal New Zealand Police College in Wellington, New Zealand on April 16, 2014.

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge, attend the mens singles final between Novak Djokovic and Roger Federer on centre court during day thirteen of the Wimbledon Championships at Wimbledon in London on July 6, 2014.

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge, watch the game between the Cleveland Cavaliers and the Brooklyn Nets at Barclays Center in New York City on Dec. 8, 2014.

Prince William, Duke of Cambridge and Catherine, Duchess Of Cambridge depart the Lindo Wing with their new baby daughter, Princess Charlotte, at St Mary's Hospital in London on May 2, 2015.

Catherine, Duchess of Cambridge, Prince William, Duke of Cambridge, Princess Charlotte of Cambridge and Prince George of Cambridge leave the Church of St Mary Magdalene on the Sandringham Estate after the Christening of Princess Charlotte of Cambridge in King's Lynn, England on July 5, 2015.

Britain's Prince William and Princess Kate, the Duke and Duchess of Cambridge, tour the Towers Residential Outdoor Education Centre in Capel Curig during a royal visit to North Wales on Nov. 20, 2015.

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge, enjoy a short private skiing break in the French Alps on March 3, 2016.

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge laugh while taking part in archery, Bhutan's national sport, in Thimphu, Bhutan on April 14, 2016.