[carton253]

Then that's how Boromir knew... because Denethor knew what Gandalf was doing with Aragorn. He probably shared it with Boromir. What do you think?

[Overtaxed]

I dunno...seeing how proud Denethor was, I think he wouldn't tell Boromir about the whole Gandalf/Aragorn thing.

[Restorer]

He probably shared it with Boromir.

I get the distinct impression Denethor never shares anything, especially knowledge he has that nobody else does.