WMG / The Full Monty

Gaz and Jean are brother and sister.

Although we never see them interact on-screen, Jean obviously knows Gaz (and his reputation) well. They also have very similar hair colour, and near the start of the film we hear Jean referred to as "Auntie Jean" by both Gaz and Nathan. While it's not at all uncommon for a British child to refer to their dad's best friend's wife as "Auntie", this troper always liked to believe that she was Nathan's actual paternal aunt.