前代未聞
Common
Noun
Noun
1
noun (common) (futsuumeishi)nouns which may take the genitive case particle 'no'
yojijukugo
unheard-of;unprecedented;unparalleled in history (unparallelled);record-breaking
犯人を弁護してた弁護士が実は真犯人だったなんて、前代未聞だ。
It's totally without precedent for the suspect's attorney to be the true culprit.