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Standard Blackwood doesn't deal with the trump king, and control-showing bids don't deal with the trump suit at all. So many partnerships prefer a variation of Blackwood that does take these cards into account.
In these variations, there are five key cards—the four aces and the trump king—to be taken into consideration, along with the trump queen, when responding to 4NT. This means that the responses to 4NT must be changed to accommodate the additional possibilities.

Some partnerships prefer to reverse the meaning of the 5 club and 5 diamond responses.
If the response is 5 clup or 5 diamond , the next suit that is not trump asks about the trump queen. Without the queen, partner returns to the agreed trump suit. With the trump queen, partner bids the cheapest outside suit that has a king, or jumps in the trump suit with no outside king.
A subsequent bid of 5NT asks partner to show a king outside the trump suit. With more than one king, partner bids kings 'up the line', cheapest first49. With no king, partner returns to the agreed trump suit at the six level.
Since key card responses to Blackwood add some complexity, especially with continuations to ask about the trump queen or outside kings, the partnership should discuss this thoroughly before changing from standard responses.