The Greek article can be used indefinitely, but this is beside the point. ΤΟΥ ΥΙΟΥ ΤΟΥ ΘΕΟΥ does not mean of God the son, but rather of the son of God, and the interlinear agrees.
Know ye not that the unrighteous shall not inherit partake the kingdom of God? Be not deceived: neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind,
I even fixed it for you @aCultureWarrior