I was exercising in the garage with my stepson but it was so hot in there I took off my tank top and yoga pants and went in just a sports bra and panties. I asked him to help me with some partner stretching and I noticed he had a huge erection! When I pointed out how hard he was he said it was because I was so hot! I was flattered that he thought his stepmom was so hot so I told him he could relieve himself on my panties. He was excited to rub his cock on my panties and pretty soon my panties were soaked from my wet pussy and his precum. It was starting to feel good to me too! Then while he was rubbing his cock "slipped" and pushed my panties to the side and penetrated my pussy. I was shocked but the feeling was overwhelming and I just wanted him to keep going! I wasn't on the pill so I told him he had to pull out. We fucked on the yoga mat until suddenly I felt warm pulses shooting inside me. Oh no! He came in my pussy! It was a huge dripping creampie. We are going to have to be more careful if we work out together again.