Sister in law caught us

My wife and I (both 33) were at her parents first New Year’s Eve. Well, we had been teasing each other and more flirty than usual all day and I guess things just came to a head. We both decided that we needed it, right then and there. So we went up to what used to be my wife’s room to fool around. After some very brief foreplay I pulled my wife’s leggings down just enough to slip myself in and started taking her from behind bent over her old bed. At some point we hear an exaggerated cough and look over to see her sister grinning. She looked at us and just said “I figured you fell asleep like everyone else, guess I was wrong” and shut the door again. My wife looked at me and just said “if she’s the only one up, no need to try and keep me quiet”. Then we fucked harder than we had been with her moaning uncontrollably as she came. A top three experience for both of us!