But

[Xinfu]

p.22
-May I speak to you? It's urgent. [...] But of course.

What does BUT mean?

[poli]

But of course means of course emphatically . In contemporary English but of course lends itself to sarcasm easily.

[Rusty]

This is a set phrase, and shouldn't be dissected.

As poli pointed out, the way it was used is just an emphatic 'of course' (an idiomatic expression in and of itself).

[Xinfu]

Excellent answers. Thank you.