In this verse Bathsheba revealed the reason of the importance of her reminder to David of his oath regarding Solomon. She stated the matter very emphatically, and it came in two parts. First, she stated the fact that Adonijah was king. Next, she acknowledged that David was unaware of Adonijah’s action.
Note that Bathsheba made no suggestion that David authorized Adonijah’s taking the throne. She assumed that the action was without the knowledge of the ruling king.
We noted before that the king’s ignorance highlighted his isolation from the matters of state that should have come to his attention, but it also emphasizes the guilt of Adonijah. It was possible for the king to give the throne to his son in his own lifetime. This is what happened with Solomon. However, there was no just way that this could be done without the king’s knowledge and consent.
18 And now, behold, Adonijah is king, although you, my lord the king, do not know it.