Proof that the "sons of God" were indeed Fallen angels and not princes or any other type of human being.

If the sons of God were anything other than angelic beings, they would not be appearing before God with Satan.

Job 1:6 1:6 Now there was a day when the sons of God came to present themselves before the LORD, and Satan came also among them.

One might wonder where the "sons of God" came from, that is to say: "how did they become fallen angels?"

To answer this question let's turn to the book of Revelation:

Revelation 12:7-9 12:7 And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels, 12:8 And prevailed not; neither was their place found any more in heaven. 12:9 And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him.

Now, keeping in mind that the Serpent (Satan) was in the Garden of Eden in the beginning with Adam and Eve, and the sons of God (Fallen Angels) were cast to the earth were also free to roam the earth.

This verse from Job 1:7 documents that Satan was free to travel freely in the world in the days of old.

Job 1:7 1:7 And the LORD said unto Satan, Whence comest thou? Then Satan answered the LORD, and said, From going to and fro in the earth, and from walking up and down in it.

In this verse in the book of Jude, these angels were of the influx that occurred after Noah's flood.

Jude 6:6 6:6 And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.