The beast who once was, and now is not, is an eighth king. He belongs to the seven and is going to his destruction. (NIV)
And as for the beast that [once] was, but now is no more, he [himself] is an eighth ruler (king, head), but he is of the seven and belongs to them, and he goes to perdition. (AMP)
And the beast that was, and is not, even he is the eighth, and is of the seven, and goeth into perdition. (KJV)