In Diamond: I hadn't been to the Battle Tower in who knows how long, so I made a team (Empoleon, Sceptile, Froslass) and went for it. I just wanted to get some more battle points to get a TM (don't recall which) and I was doing well. I had beaten the 6th Trainer when the lady tells me "The Tower Tycoon would like to challenge you" (or something along those lines) and I was all "What!?" D8 ...
In the end, I ended up beating him (who knows how I managed that as my team, aside from Froslass, wasn't even trained properly...) and I felt awesome. 8D
Haven't reached him for the rematch though.