She was a friend of my parents from when I was small. I think she was my db's godmother, and my Dad was one of her son's godparent. My parents were friends with her and her dh.
She shagged my Dad under my Mum's roof whilst holidaying with them (my parents lived out of the Uk for a couple of years), and were seen canoodling in a public setting. Friends of Mum tried to tell me, but I thought they meant a previous affair Dad had had.
My parents divorced, as did he and her husband (who was lovely) and I was saddled with my Dad's new wife at 24. I was married, refused to acknowledge her as anything to do with me, and refused to play ball when my Dad tried to revise family history to replace my Mum with her.
I refused to go to their wedding as I didn't want to 'welcome her to the family', and I couldn't sit there making nice and playing happy families when I was feeling so stabby towards them both. My ds had as little to do with her as I could manage, and any requests that she be called 'Nana' or 'Granny' were met with the response that she wasn't his grandmother, and the two who did exist would take it very badly if she were referred to as that. If my Dad, db etc wanted to deal with my Mum and mil on the warpath, then they were welcome.
I think I last spoke to her at my grandmother's funeral in 2006, which was 5 years after my Dad had died, and I hadn't spoken to her between the two funerals.