IPA: /ʌnˈflætərɪŋli/
KK: /ʌnˈflætərɪŋli/
In a way that does not show someone or something in a good light; not flattering.
The article described the politician unflatteringly, highlighting his mistakes and failures.
Unflatteringly → It is formed from "un-" (meaning not), "flatter" (from Old French *flatter*, meaning to praise excessively), and "-ingly" (meaning in a manner). The word describes a manner that does not praise or is not flattering.
Think of 'not' ('un-') praising someone ('flatter') in a certain way ('-ingly') — that's why unflatteringly means in a way that is not flattering.