Grandmother for a visit - Short story

It is weekend and grandmother is there for a visit. Peter, her grandson, is going in the bathroom. "Oh, I didn`t know you are in here", he says to his grandmother. She smiles and locks the door. Peter looks confused and wonders what that means.
"During the last few weeks I noticed you looking at me this special way", granny says. She walks very close to her grandson and caresses him between his legs. "Oh, you are getting a bulge", she says amused.
Peter doesn`t know what to say and gets a red face.
"Don´t be shy", his grandmother says and rubs her hand on his bulge. She opens the zipper and takes out Peters erected cock. "That`s a nice one and I`d like to know if it feels like that", she smiles.
"Come and fuck me", granny asks Peter. The very next moment she pulls down the boys trousers and panties. His erected cock stands ready for it.
"But...", Peter can`t say more. His grandmother asks him what his problem is. She lifts her dress and takes off her panty. "Push it in. I know you want it and your cock too", the woman demands.
Peter sees his grandmothers cunt and he can`t resist.