As intensifiers (words that make an adjective stronger), adjectives are used very often instead of adverbs in English.
For example:
bloody stupid (U.K.),
wicked cold (Boston),
dead certain.
If you said bloodily stupid in England, wickedly cold in Boston, or deadly certain pretty much anywhere, it would sound real funny. People say real hot but don't often say real true, because real is an intensifier in the first but not the second. (See Google Ngram).