( informal , ironic ) used when you are saying that sth is very unlikely to happen :
Paul? Apologize? That'll be the day!
( informal , ironic ) used when you are saying that sth is very unlikely to happen :
Paul? Apologize? That'll be the day!
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005