What flabbergasted, and then deeply wounded, him was the refusal of his journalistic colleagues to stand with him as he pressed for correction of the demonstrable falsehood.
The verb form, amaze, means "to overwhelm with surprise or sudden wonder; astonish greatly," and its synonyms include astound, astonish, shock, dumfound, stun, and flabbergast.
His knowledge is flabbergasting, but the thing that makes him great is his strength of conviction balanced by his interest and openness to the views of others.