Frederik of the Netherlands (middle name Karel)
1797-1881 Netherlands

Willem, Prince of Orange (middle name Karel)
1849-1879 Netherlands

Baudouin of Belgium (middle name Karel)
1869-1891 Belgium

Charles of Belgium (a.k.a. Karel)
1903-1983 Belgium

Leopold III (middle name Karel)
1934-1951 Belgium

Baudouin of Belgium (middle name Karel)
1951-1993 Belgium

Gabriel of Belgium (middle name Karel)
2003- Belgium
