Oh parents tell their kids secrets all the time. Sure, sons and daughters make a fuss, but it's what parents do--sticking their noses into their kids lives even when their kids grow up. Any other adult couldn't get away with that--but parents can and do. That's why Joe would be the one to tell, because he can take the risk--he knows he's never going to lose Iris--or Barry.
Have you people never read A ROOM WITH A VIEW--or at least seen the movie?