I have a very simple question, how can "Didn't he used to be great?" be correct? Why is the past tense marked twice? Is it because the verb is "used to"? Because I thought it was "use to", normally used in the past because of its very meaning but still subjected to the same rules as other verbs regarding modal verbs that absorb the past markers like "did".
Thanks in advance!
EDIT: Forgot to say, saw this in a newspaper in London and was told by two native speakers it was correct.