I have a bet on this: Learnt is a real word, right?

Right you are. If you're writing or speaking in British English, you're likely to use learnt as the past tense or past participle of the verb learn. In American English, you'd probably say learned. Both forms are correct, as are other verbs that carry the option of an added "ed" or "t" — burned/burnt, leaped/leapt, dreamed/dreamt, and more.

From Thomas Hardy's The Return of the Native:

He hoped that the worst would soon be over; but at the surgeon's third visit he learnt to his dismay that although he might venture out of doors with shaded eyes in the course of a month, all thought of pursuing his work, or of reading print of any description, would have to be given up for a long time to come.

And from Robinson Crusoe, by Daniel Defoe:

It was my great misfortune that in all these adventures I did not ship myself as a sailor; when, though I might indeed have worked a little harder than ordinary, yet at the same time I should have learnt the duty and office of a fore-mast man, and in time might have qualified myself for a mate or lieutenant, if not for a master.