I had sex with my brother in law..??

So I had sex with my now fiances brother like 6 years ago. It was a one night stand and a drunken night. My fiancé and I met later on, like 2 years after that, and I had no idea he was his brother. Anyways a couple of months into our relationship I had met his entire family and his brother was there. Obviously I was mortified and so was his brother. I told my fiancé about it that night. He was grossed out and kind of distant for a few weeks, but said it was the past and as long as there was nothing there he could get over it lol. He and his brother were never close, as his brother lived with his dad.

Anyways now my fiance and I are getting married soon and I feel really weird about the fact he’s about to be my brother in law and we had sex years ago. Is this weird? How would you feel in this situation? Should I feel ashamed? Because I kind of do. Ive never felt this way before, and I know my fiancé is completely over it and doesn’t care. I almost feel like this is incest. I mean I know it isn’t obviously, but that’s how I feel. Has anyone else been in this position?