There's a certain… awkwardness between Alan and Gary on the Prisoner of Azkaban set, which, thankfully, the tabloids haven't noticed. Even if they had, they'd never work out the cause without being tipped off. Would think it had to do with the animosity between their characters, or something equally ridiculous.
They'd never guess the truth. Never guess what really happened at the wrap party for Fallen Angels, which was the last time they worked together. Too much to drink, and a sudden fit of mutual lust. And a cold and silent parting, next morning.
They never talked about it, or much else, again.