They are also seven kings. Five have fallen, one is, the other has not yet come; but when he does come, he must remain for a little while.
The beast who once was, and now is not,1 is an eighth king. He belongs to the seven and is going to his destruction.
References for Revelation 17:11
"The ten horns2 you saw are ten kings who have not yet received a kingdom, but who for one hour3 will receive authority as kings along with the beast.
References for Revelation 17:12