Tricking your sister into throat fucking

You go to the same costume party that you know your sister will be at. You wear a mask so she can't recognize you! After some small talk she insists you go some place quite and more ... she throws herself at this mystery man which is exactly what you wan. She keeps asking you to take your mask off so she can see who's dick is in her mouth... you reveal yourself and all though she seems disgus and upset she doesn't stop. She says you have to throat fuck her until you cum.