My mother just called to tell me that my sister Julie gave birth to a baby girl a few minutes ago.
The entry title is how I responded to the news.
It’s an allusion to an old joke:
John: I just got a telegram saying my sister gave birth to a baby.
Bill: That’s great.
John: Yes, but it doesn’t say whether the baby’s a boy or a girl, so I don’t know whether I’m an uncle or an aunt!