My mother in law was staying with us for a few days. One morning my wife left for work and it was just me and her mother. She actually came into my bedroom, sat on the bed and began to talk to me. During our conversation she mentioned she was a little cold and I made a joke about it being warm under the covers but she would see more than she ever should. She seemed a little confused with what I said and asked what I meant. Before I had a chance to explain she pulled back my covers and there I was laying naked in front of her. It was unexpected and I was a little embarrassed. She pulled the covers back over me and suggested we not mention this to my wife. I agreed because I didn't know how my wife would react. She then asked how I felt with what just happened. I told her it was unexpected but I would get over it. She mentioned she was cold again and asked if I would mind her getting under the covers with me. She added it was just to keep warm and since the covers would be pulled over us nothing would be exposed. I agreed and she mentioned we best keep this to ourselves and tell no one. I expected her to just jump in with her robe on but she really surprised me when she removed it first. She was wearing nothing under her robe and was now under the covers naked with me. We began talking like it was no big deal. A few minutes after us under the covers together she took a look under the covers and asked if I had ever expected to see her naked. I truly didn't and told her so. She told me she never expected to see naked either and especially with the way I currently was. I don't know what she meant but with her next question I did. She asked if me seeing her naked caused it. That's when I realized I had a hard on and she saw it. I told her she sort of was the cause. She apologized for staring at it and I told her I didn't mind and would stare too if I had the chance. She then told me she had never done this before and showed me her tits. I was in awe of her tits but then she sat up on the bed and showed me her private area. She pushed the little hair she had to the sides and told me to come in for a closer look if I wanted. I was only inches away and she was showing me her very intimate part including a look at her swollen clit. She then got back under the covers and told she can't believe she just displayed herself like that to me. I told her I liked it and she said it was very easy to see that I was. She said she better go because she could easily see this leading to more and didn't want to have the guilt of having to keep from her daughter that her son in law had his cock in her pussy. She left and I was left very aroused. I went to the bathroom and began to masturbate. I was doing it at the sink and had cum quickly. She was at the open door and had seen everythig that I had just done but just walked away after. Shortly I could hear moaning from her room and I went to see if she had left her door open too but it was shut. I stood at the door and the moaning became louder and it was very clear what was happening on the other side of it. After the moaning stopped I went back to my room and fell asleep for awhile. When I woke up she was already awake and we talked about what happened. She made me promise to never tell anyone how she showed me her pussy and clit because she was very embarrassed about it now and didn't know what came over her. I promised and that was basically it.