joking apart/aside

(all) joking aside

 and (all) kidding aside
being serious for a moment; in all seriousness. I know I laugh at him but, joking aside, he's a very clever scientist. I know I threatened to leave and go round the world, but, joking aside, I do need a vacation.
See also: aside, joke

ˌjoking aˈpart/aˈside

(British English) used to show that you are now being serious after you have said something funny: No, but joking apart, do you think we should go and see if she’s OK?
See also: apart, aside, joke