Dictionary / Vocabulary / とうの昔
とうのむかし
a long time ago; long ago
Also written 疾うの昔、当の昔、遠の昔
こいつがそんな玉じゃないことなんてとうの昔に解っていたからさ。
That's because, you see, I've known he isn't that sort of person from a long time back.