She Wants to Date Her Stepdad-OPP

A woman has developed feelings for a man who was once her step father. She wants to pursue a relationship with this man but is worried how her mom will take the news.

Mike & Kate,
I could use some advice on a situation I can't talk with any of my friends or family about. I figured advice from people who are detached from the situation would be better.
I am thinking about getting into a relationship with my step father. He's actually my ex step father. He was my mom's second husband (she's on #4). They were married about 10 years ago. I was in college at the time (out of state) and didn't really get to know him that well. We never lived in the same house. I would spend most of my summers working and only came home for holidays. They were only married 3 years so by the time I graduated and moved back here, he and my mom had divorced.
Fast forward 10 years. We ran into each other last fall at a fundraiser. It started as just getting together for coffee and catching up. We both really enjoyed each other's company and continued to see each other over lunches and dinners. Nothing romantic happened until after the holidays. After a couple of weeks of spending time with him I realized I was developing feelings for him. Then a few weeks ago, he kissed me. I felt like fireworks were going off in my belly. He is a very handsome, charming man. Even though there is a 20 year age difference, we connect on so many levels. We both want to pursue a relationship. The problem is I don't know how my mom would react. He was the one to divorce her. But that was 10 years and 2 husbands ago. My mom and I have a good relationship. We aren't best friends like some mother/daughter relationships. She has always been more focused on the men in her life.
I was hoping that with OPP I could get people's opinions. How would you react if you found out your daughter was dating your ex husband? Ladies would you date a man who was married to your mother? Has anyone else ever dated an ex-step dad?

Thank You