Is there a word or simple phrase to describe the relationship between yourself and a step-parent's ex-spouse? Particularly, I'm seeking to address the case when the ex-spouse is a parent to your step-sibling.
Example: Bob’s mother re-married to Alice’s father. How should one appropriately refer to the relation between Bob, and Alice’s mother?
I’m trying to find something that’s appropriate for a relationship closer than “Bob’s step-sister’s mother” or “Bob’s step-father’s ex-wife” but not quite so close as to just call her “Bob’s mom”.