From Longman Dictionary of Contemporary Englishdisillusiondis‧il‧lu‧sion /ˌdɪsəˈluːʒən/ verb [transitive] DISAPPOINTEDto make someone realize that something which they thought was true or good is not really true or good I hate to disillusion you, but I don’t think she’s coming back.→ See Verb table
Examples from the Corpus
disillusion• Some may be converted and disillusioned, others will be unconverted but believing or searching people.• I hate to disillusion you, but you'll probably never get your money back from them. 