Oh, that's — when I was a fragile hothouse flower in Hightown, my aunt wanted a guardian in the house and I decided to presume on his — very former — connection to my uncle to piss her off by choosing a mage.

( it's a little convoluted, although familiar enough and easy to rattle off that she's clearly picked up again from where she'd been much struck by the news. )

Resultingly, every now and again he comes over all avuncular.