From Longman Dictionary of Contemporary Englishknow different/otherwiseknow different/otherwiseinformal to know that the opposite of something is true He told people he didn’t care about her, but deep down he knew different. → know
Examples from the Corpus
know different/otherwise• Christopher would tell me all sorts of things I would never know otherwise.• Just another wench, he told himself angrily, but deep down he knew different.• Now, presumably, they know different.• The answer is probably no - but do you know otherwise?• The public may think the law applies only to the most dangerous offenders, but inmates know otherwise.• We knew otherwise - and told you so on October 26,1990.• If you know different contact: who would like to get this year's books completed.• We teach them, you know different things. 