A little *****t fantasy of mine

i arrive at my masters house. I'm led to the bedroom, stripped naked, tied spread eagle to the bed, a cock ring is placed around my already stiffening cock and a ball gag inserted in to my mouth. My master then informs me that he has a nasty little surprise for me. He leaves the room and returns with my sister, completely naked, blindfolded and hands cuffed behind her back. She is helped to climb onto the bed and straddle me, I try to protest as she is lowered onto my cock, but all anyone can hear is muffled sounds due to the gag. I come almost immediately as she starts riding my cock, but due to the cock ring my erection refuses to disappear. It is obvious that my sister has no idea that it is me she is riding and the more i try to fight and protest, the more she seems to be enjoying herself. My master climbs on the bed behind my sister and with pure force shoves his cock in to my sisters ass. She screams in pain, but still doesn't stop riding me. This goes on for about 10 minutes, when i suddenly sense that she is getting close to cumming, as well as me. My Master must sense this as well as he whispers into her ear "time to take the blindfold off bitch, so you can see the cock you've been so eagerly fucking." The blindfold is removed and the look of sheer terror and pleasure combined on her face as she realises she is cumming on her own brothers cock is priceless. I can hold back no longer and again fill her pussy with my cum as i feel my master cumming in her ass.