What is the dramatic irony in Duncan saying "all I can say is that I owe you more than I can ever repay"

The dramatic irony in Duncan saying "all I can say is that I owe you more than I can ever repay" is that he is about to be killed by Macbeth, so he will repay him for his courage with his life. A dramatic irony is a situation in which the audience knows something that the character ignores. So the words of the character that doesn't know what is really happening have a completely different meaning for the audience. In this case, the meaning is just the opposite because Macbeth, after the witches told him that he would become king, has started to think in murdering Duncan.