The world of ZR is a shared one with a few comics, some that have stopped updating, but one that still is going is D20Monkey. In that comic Brett has become Santa, taking the mantle from his father. This happened years ago, around the time of the George/Santa throwdown... but ZR has never addressed the change. Part of this arc's reasoning was to rectify that as Santa, now Kris, was an established thing in ZR.
So yeah, go read Brian's comic. It's good.
Buy a shirt from his store. I did. I actually own three of his shirts.