Could you please shed light on what this means? Can GOD have a God?
Psalm 45: 6 'Your throne, O God, is forever and ever; the staff of Your kingdom is a staff of righteousness. 7 You love righteousness, and hate wickedness; therefore God, Your God, has anointed You with the oil of gladness above Your fellows'.
Great question! Let's take a look at this from the Hebrew perspective:
English does not convey the meaning of the verse very well. In this psalm we read: "6 Your throne, O Power (Elohim = King), is forever and ever; The scepter of your kingdom is the scepter of equity. 7 You love righteousness and hate wickedness; Therefore, Elohim [King], your Eloheicha [supreme God], has anointed you with the oil of joy above your peers".
It was common in the ancient near East for the mortal human judge or king to be addressed as "Elohim" (Powerful One = God). As Rashi points out, "...even a mortal man of flesh and blood can merit this divine title (Elohim) if he seeks to administer God's justice on earth, as we read concerning Moses, 'Behold I have placed you [as] 'Elohim' over Paroh [Pharaoh]' (Ex. 7.1)".
So, it is understandable that King David (and later, Yeshua) was addressed as "Elomim" (unfortunately, only translated as "God" in English); but, it must not be forgotten that this human, mortal "Elohim" ("God") who died for us, was anointed by his "God" - The Creator of the universe.