In a disbelieving manner; in a manner that is difficult to believe(adverb)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "disbelievingly" in a sentence
"Things can get awkward, as with the "disbelievingly," and on page 100 we get "asked exasperatedly.""
"Walter listened disbelievingly as O, affecting his familiar attitude of solicitous older brother, encouraged him to see the bright side in the bewildering estrangement proposed."
"I tell the girls the wedding is back on and they look disbelievingly at me."