Three weeks back I was on the bus home after visiting a friend of mine. The route takes me past my uncles house and I noticed my moms car parked outside. Thinking I could ride home with her and not have to walk the half mile from the bus stop, I got off and walked up to the house. Thinking as usual my uncle would be in his back yard fixing some part of a motor cycle, I went around back. No one was in the back yard but his back door was ajar. Walking in I heard what I thought to be a movie on the tv, then realised the sounds were of someone having sex. Never thinking it could be anything bad, I just walked into the front room and quickly backed out. What I saw was my mom lay over a small coffee table, completely naked and squatting behind her was my fathers brother. He was also naked and he was fucking my mom in the ass. The didn't see me as they were facing the other way too busy fucking and for what must have been two or thre minutes, I watched in disbelief as my uncle slammed his cock into my moms ass. She was almost begging him to fuck her harder and when he started to slap her ass aswell, calling her HIS dirty fucking slut, I walked out. The crazy thing is I'm sure my dad has been dropping her off at his house some evenings. Picking her up later when she rings. Now I don't know if my mom is having an affair with my uncle without my dad suspecting anything. Or does he know his brother is fucking his wife. Man this all so messed up. I don't know whether to tell my dad or keep right out of it, strangely hoping my father accepts what is going on.