IPA: /ʌnˈfeɪndɪdli/
KK: /ʌnˈfeɪndli/
In a way that is sincere and genuine, without any pretense or deceit.
She unfeignedly expressed her gratitude for the help she received.
Unfeignedly → It is formed from "un-" (meaning not) and "feigned" (from Old French *feindre*, meaning to pretend or to make a false show) and the adverbial suffix "-ly" (meaning in a manner of). The word "unfeignedly" means in a manner that is not pretended or false, indicating sincerity.
Think of 'not pretending' ('un-') and being 'sincere' ('feigned') — that's why unfeignedly means to act sincerely.