What is Macbeth's reaction when Duncan reveals his plan to name his son Malcolm as the heir to the throne

Macbeths reaction is to prevent Malcolm from becoming king - leading him to think about committing murder and treason. "The prince of Cumberland: that is a step On which I must fall down, or else o'erleap For in my way it lies." this is showing how Malcolm is in his way of becoming king as the witches prophesied.