The United KingdomPrince Charles, Prince of Wales and Camilla, Duchess of Cornwall watch the 'Campai...

1. Royal Heirs Around the World Photos
The United Kingdom
Prince Charles, Prince of Wales and Camilla, Duchess of Cornwall watch the 'Campaign for Wool
Lamb National' sheep race as they attend The Prince's Countryside Fund Raceday on March 29,
2015 in London, England.
Max Mumby/Indigo/Getty Images
The United Kingdom
Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge on March 27, 2015 in
London, England.
Chris Jackson/Getty Images
Spain
Princess Leonor attends Easter mass at
the Cathedral on April 5, 2015 in Palma
de Mallorca, Spain.
Europa Press via Getty Images
Belgium
Queen Mathilde of Belgium, left, and
Princess Elisabeth, Duchess of Brabant
arrive at Sint-Jans Berghmans college to
attend the first of the day of the school year on Sept. 1, 2014 in Brussel, Belgium.
Mark Renders/Getty Images
Denmark
Crown Prince Frederik, and Crown Princess Mary of Denmark, with their children, Princess
Josephine, Princess Isabella, Prince Vincent and Prince Christian appear on the Balcony of
Amalienborg Palace on The 75th Birthday of Queen Margrethe II of Denmark, on April 16, 2015 in
Copenhagen, Denmark.
Julian Parker/UK Press via Getty Images
Sweden
Crown Princess Victoria of Sweden and Prince Daniel, Duke of Vastergotland attend a photocall on
Princess Estelle's first day at pre-school on Aug. 25, 2014 in Stockholm, Sweden.

2. Mark Cuthbert/UK Press/Getty Images
The Netherlands
Crown Princess Catharina Amalia of the Netherlands, leaves the Royal Palace after having brunch
with other guests on May 1, 2013 in Amsterdam Netherlands.
Michel Porro/Getty Images
Norway
Crown Prince Haakon of Norway and Crown Princess Mette-Marit of Norway with Princess Ingrid
Alexandra, Prince Sverre Magnus and Marius Hoiby greet the Childrens Parade on the Skaugum
Estate on May 17, 2014 in Oslo, Norway.
Mark Cuthbert/UK Press via Getty Images
Monaco
Prince Albert II of Monaco and Princess Charlene of Monaco present twins Princess Gabriella of
Monaco and Prince Jacques of Monaco at the Palace Balcony on Jan. 7, 2015 in Monaco.
Villard/Niviere/PLS Pool/Getty Images
Luxembourg
Princess Stephanie of Luxembourg and the hereditary Grand Duke Prince Guillaume of Luxembourg
visit the state chancellery on Aug. 31, 2013 in Wiesbaden, Germany.
Thomas Lohnes/Getty Images
Thailand
Crown Prince Maha Vajiralongkorn of Thailand, heir apparent to the Thai throne, and his sister
Princess Maha Chakri Sirindhorn arrive at the Nieuwe Kerk in Amsterdam for the inauguration
ceremony of King Willem Alexander of the Netherlands, on April 30, 2013 in Amsterdam,
Netherlands.
Julian Parker/UK Press via Getty Images
Japan
Crown Prince Naruhito of Japan speaks during a press conference on June 19, 2014, in Neuchatel,
Switzerland.
Sebastien Bozon/AFP/Getty Images
Saudi Arabia
US Secretary of Defense Leon Panetta, right, meets with Prince Muqrin bin Abdul Aziz, left, Minister
of Intelligence for Saudi Arabia, during a condolence call at the Royal Court June 20, 2012 in Jeddah,

3. Saudi Arabia.
Pablo Martinez Monsivais-Pool/Getty
Images
Jordan
Jordan's Crown Prince Hussein bin
Abdullah, right, and Prince Ali Bin Al
Hussein, left, wave as they attend the 2014
World Cup qualifier match between Jordan
and Oman in Amman on June 18, 2013.
Crown Prince Hussein bin Abdullah is the
heir apparent to the throne of Jordan.
Khalil Mazraawi/AFP/Getty Images