Walter forgot this was his siter standing there before him his hormones went wild, and he went wild too!
Stepping to be before his sister he began to touch he and be overly friendly, feeling her as if she was some kind of cheap bimbo.
"What is your third wish, my misstress master?" asked the Genie, seemingly bored by the puny minded wishes that he had just fulfilled.
Jenny began to slap and swat at the asserting ahnds of someone enthralled with the female that stood there looking all nice and willing.
"Damn you Walter, your acting like some Jackass in season! I don't want you to play with my body, go find some other jenny and make love to her. Genie, Genie, send Walter to be passionate to some other Jenny and not like me!" spoke an infuriated Jenny.
"It that your wish?" asked the surprised and smiling Genie.
Even as Walter faded from her sight she saw him change from a hulk of a man to become some large blonde Jackass, it having a massive erection and then was gone.
"What happened, where is Walter?" asked a stunned and struck Jenny.
The Genie stood and smiled for a moment and began to turn again into his cloud of smoke.
"No, wait, I command you to tell me what you did with Walter!" demanded Jenny her eyes burning with fear and horror of what she was a witness.
The Genie took a more solid form, speaking with a still half grin and smirk, he announced to Jenny, "As with your wish, Walter your brother has ceased to exist. He and his memory is changed! Walter thinks now of only what would satisfy his inner lusts and needs. Whether he is hungry he grazes until full, when he smells the scent of a mare or jennet in season he becomes a virile stud. Otherwise, he works for his keep, being in harness he works beside three others like him, they pull a heavy wooden wagon. His beastly body is strong and healthy to the extreme. His male virility is something a mark of his breeding, a Morgan mare mother and his father like him an Andulsian Jack of some renoun!"
"Bring him back here now," demanded Jenny as tears of fear for her own foolish wish welled in the corners of those loving eyes.
The Genie cocked his head and gave her a wondering gaze. then taking a deep breath he said, "Sorry, not possible, Walter is gone, what he was, is no more and from your own lips your sent him into exile, transformed to seek a jenny for his male pleasure, your wish was profound and he is as he shall remain, a Jackass at stud!"