As Charlie started to pull off his shirt he could feel a burning sensation start in his balls. He could also feel himself starting to get hard. But at the same time it felt different, he felt harder than normal. Looking down after taking off his shirt, he could see the imprint of his hard erection in his jeans. He seemed bigger than normal, and could feel it getting bigger. As this happens his balls are also swelling in size, making him feel hornier.
Making him scramble to get his work boots off of his feet. As he bent forward to undo the laces and pull them off, he could hear the fabric of his pants splitting apart. Eventually splitting apart along the crotch seam. As he gets his left boot off of his foot he can feel a pressure building at the base of his spine. As he is undoing his right boot he can feel something growing off of his spine causing him to grunt as it starts to fill up the back of his underwear.
As he was pulling off his last boot he could feel his underwear start to tear by his still growing cock. Eventually breaking free from the constraint of his underwear. Followed not too much longer by his tail, which was starting to sprout long black hair.
As Charlie stared at his growing cock he could see the head of his penis start to flatten out, while it was turning black with a large pink splotch along the shaft. Quickly his feet caught his attention when they started to grow and split his cotton socks open. As he down at his growing feet he could see his toes growing together and his toenails turn black.
There was no doubt in his mind that he was becoming a horse. As he looked up he could see his former wife's mare Ginger with her tail raised winking her vagina at him. As he saw this he got unbelievably horny. He knew what he had to do, so he worked his way over to her as his feet were in their final stages of becoming hooves. As he was pushing his now equine penis into her wet and inviting pussy he could feel his face starting to push out into that of a horse while brown fur started growing all over his body. He could also feel his hair growing into a long black mane.
As Charlie was thrusting into her pussy, he could smell her with his new muzzle, and how aroused she was. He was intoxicated by it, and couldn't get enough of it. While he was thrusting away he could feel a churning sensation in his large equine testicles. Before he could fully grasp what was happening he could feel himself orgasm twice. Neighing proudly both times.
He found he liked his new equine form, but knew he couldn't go out in public as a humanoid horse without causing some panic and the government wanting to capture him for study.