OK, so Kate may be missing the sexual attentions of her husband, and Kelly appears not to have a girlfriend at the moment; so together with the perceived naughtiness of him wearing feminine attire and the inhibition lowering effects of the wine, I can sort of see how this scenario arose.

However, for the sake of good storytelling, I hope this is more-or-less a one-off event - especially given they're relations and there's probably a twenty year age gap between the two.

Anyway, let's see how things play out in the morning...