Prank on my busty stepmom ends with her secretly riding my cock

I see my busty stepmom in the bathroom and I can't help fantasizing about those big tits she has in my face, so to see her naked I take her clothes and run out. She comes out angry because she's cold, but what she didn't know was that she would see my hard cock, so we get horny and end up fucking hard without anyone seeing us.