Rex Deus 

Said to a name that a group of European families use to identify themselves.  They have an oral tradition that they descended from the twenty-four high priests of the Temple of Jerusalem of the the time of Jesus. This priestly class is said to have been hereditary and was drawn from the tribe of Levi.

They are said to keep their bloodlines clean by restricting marriages to members of these families.

(See Templars in America, page 10-11)

The author of this website has no idea if this is true or not.

Some of the families involved are said to be:
    Counts of Champagne
    Lords of Gisors
    Lords of Payen
    Counts of Fontaine
    Counts of Anjou
    de Bouillon
    St Clairs of Roslin
    Brienne
    Joinville
    Chaumont
    St Clair de Gisor
    St Clair de Neg
    The Hapsbergs

This group is said to have been formed by Godfrey de Bouillon who was a descendant of Jesus Christ and is said to have preserved his bloodline to this day.

(This information came from "The Second Messiah" p 79)