Not too late yet, I hope...
The quote comes from
Farmer Giles of Ham and is spoken to Giles by the King. Did you expect his full name as the answer?
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'Mercy!' cried Gandalf. 'If the giving of information is to be the cure of your inquisitiveness, I shall spend all the rest of my days in answering you. What more do you want to know?' 'The whole history of Middle-earth..
.'