Is this what you were after?
I'm pretty sure that he does. He was stating that he was lost in his secrets (ie magic) and that he lost control of the kingdom....*twiddles fingers* ill see if i can find it quickly, hmmmm the only quote i could quickly find wasn't near act 5. It was Act 1 scene 2 actually, around the line 66 pssh ill type it here for you ^.^;
Prospero - " My brother and thy uncle, called Antonio - I pray thee mark me, that a brother should be so perfidious! - he, whom next thyself of all the world i loved, and to him put the manage of my stat as at that time through all the signories it was the first, and Propsero the prime duke, being so reputed in dignity, and for the liberal arts without a parallel those being all my study, the government I cast upon my brother, (probably most important part as it actually uses first person to state that it was him handing the government to his brother...anyway...i shall continue) and to my state grew stranger, being transported and rapt in secret studies. Thy false uncle - Dost thou attend me? "
Then Prospero continues on to ramble to Miranda like you would expect.
I also had a quick read through Prospero's main solliloquys but failed to find anything that distinctively related to the fact that it was his negligence that exiled him from his Dukedom. =)
Hope that helped, was a good little study for myself aswell finding some nifty quotes ^.^; so I thankyou first ^.^; I am using The New Penguin Shakespeare version but that shouldn't matter which is why i gave you lines instead of pagenumbers ^.^;
