Stepbrother's secret spying leads to forbidden anal encounter with teenage sister

Stepbrother and I were chilling on the bed, and my sister came in and started teasing us. She was playing with her feet and making silly faces. My stepbrother was secretly spying on my sister, but I didn't know about it. We all were laughing and having fun, and then she started to seduce him. She was asking him to teach her how to ride a bike and stuff like that. He was trying to resist, but she was so damn hot. So, he finally gave in and started teaching her. I was not really surprised, because I knew that my sister has a big ass and she is very sexy. So, they started to fuck and it was very hot. She was riding his big dick and he was fucking her hard. In the end, he came inside her and it was a very nice experience for both of them.