List of current reigning monarchs by length of reign

This is a list of reigning monarchs sorted by length of service. This list includes monarchs who do not reign over entire nations, such as Muhammad V of Kelantan, but does not include pretenders, such as Simeon II of Bulgaria; monarchs without physical territories such as the Prince and Grand Master of the Sovereign Military Order of Malta; constituent monarchs such as traditional African rulers; or monarchs whose position is unofficial, such as Tenzin Gyatso, 14th Dalai Lama.

Source: Wikipedia — List of current reigning monarchs by length of reign (CC BY-SA 4.0)