If you are applying in person then you wouldn't need to prove that you have met, but you might want to bring a couple of time dated photos or letters from friends proving the length of the relationship. It is not going to be essential if there are no prior immigration complications.
Also, you obviously won't need to bring a certified copy of his passport, as he will be able to bring the original. It is, however, a good idea to bring a normal photocopy of the details page, just to save them the hassle.
Vicky
