A very good experience
I have a sister who is four years older than me. She is very beautiful and I dream to see her masturbate. One night I was so excited I looked in her hamper and found a dirty string. I sniffed the crotch and masturbated with it coming into the material. I left it on the top of the hamper.
Before I went to sleep I returned to her bedroom and I found the string sticking out from under her pillow. I took it wanting to cum on it again and laid the string on her bed. My sister was in the bathroom. But suddenly she opened the door and saw me rubbing my hard cock.
I was so excited seeing her I came, grunting very loud and cumming hard on the string and on her bed. My load was very rich, with a lot of cum.
My sister closed the door and said 'Wooh, oh my god' She was naked under her robe. She opened it and stood staring at me and she rubbed her clit very quickly and in a few minutes she came too in front of me.
After, we laughed together and we said we must do that again.