That'll be the day!

that'll be the day

Said of something that is unlikely to happen. A politician speaking the truth? Ha, that'll be the day!

That'll be the day!

Inf. It will be an unusually amazing day when that happens! Bill: I think I'll fix that lamp now. Andy: When you finally get around to fixing that lamp, that'll be the day! Sue: I'm going to get this place organized once and for all! Alice: That'll be the day!
References in periodicals archive ?
That'll be the Day! 1950s Newcastle, through Tyne Bridge Publishing, is on sale now.
That'll be the Day! 1950s |Newcastle, through Tyne Bridge Publishing, is on sale now, priced PS13.