1 Queen Elizabeth II:
Monarch of the United Kingdom, she has been on the throne for 62 years.
2 King Juan Carlos: The Spanish monarch has announced he is to abdicate in favour of his son Felipe.
3 King Philippe: The 54-year old ascended the Belgian throne in 2013.
4 Prince Albert of Monaco: He is the son of Prince Rainier and the Hollywood actress Grace Kelly.
5 King Willem- Alexander: Became king of the Netherlands 2013 when his mother Queen Beatrix abdicated.
6 Queen Margrethe: The first female ruler of Denmark since the 1400s, she was crowned in 1972.
7 King Harald of Norway: He became king in 1991 on the death of his father Olav.
8 Prince Hans-Adam of Liechtenstein: He has ruled the tiny European principality since 1989.
9 King Carl Gustaf: The Swedish king has reigned over the Scandinavian country since 1973.
10 Grand Duke Henri of Luxembourg: Ruler since 1990 and a first cousin of King Philippe of Belgium.