Alison Gilbert covered her mouth with her hand to stifle the gasp that nearly escaped. The 45 year old mother of three was standing outside the bedroom door of her 19 year old son, Jason, unable to fully process what she was seeing through the thin crack between the door and its frame. There, laying on his bed, was Jason. But he was not alone. He was laying on his back naked, and straddling him equally naked was his 25 year old sister Sarah.
Just minutes ago Alison had been working out in the family home's basement as she did for 2 hours every day. After only an hour today, however, her AirPods had died and she had made her way back upstairs to charge them, vowing to continue the second half of her workout once they were fully charged. To her surprise as she approached her son's bedroom door she had heard moaning, and seeing that his door was open a crack she could not resist peaking. The moans had been unmistakably female, and she was curious if Jason had a girlfriend that he was hiding from the family.
She had definitely not been expecting to see her eldest daughter slamming her voluptuous ass down on her only brother's sizeable cock. Sarah was riding Jason like a woman possessed, her back to the door and her generous curves rippling with the force of their fucking. Although she couldn't see from this angle, Alison assumed that Jason's hands, and maybe his mouth, were full of Sarah's enormous tits. The mother could feel her pussy moistening at the sight of her two eldest children committing incest. Her mind was a whirlwind of contradictions. Her logical brain knew she should walk in and stop them. But the rest of her brain was experiencing two very strong emotions that kept her frozen in place. One was horniness, horniness like she had never felt in her life. The other was fear, fear of what she might do if she crossed the threshold into her son's room.
Despite herself, Alison found her hands wandering over her own generous curves as she watched the siblings fucking. She began rubbing and pulling on her nipples through the thin sports bra she wore during her daily workout sessions in the basement. She was about to stick her hand down her leggings and rub her throbbing clit when she heard Jason moan much louder than he had been, and Sarah said something that made her mother freeze in place.
"That's it baby, cum for mommy. Cum deep in mommy's pussy."
Alison could see her son's cock throbbing in his sister's pussy as she said those words, could nearly follow the journey of his load as it sped from his swollen balls up the impressive length of his shaft and deep into the eager womb awaiting it. She had to bite her lip to keep herself from moaning out loud as the combinations of her hands pinching her hard nipples and the forbidden sight in front of her brought her to orgasm. She felt her own juices soaking the front of her leggings, all without laying a hand on her long neglected pussy. Coming to her senses, she looked into the room again to see Sarah and Jason making out furiously, caught up in the post-orgasm passion of their incestual fucking. Alison crept away from the door, back down to the basement as quietly as she could before either of the siblings realised that had been watched.
Down in the basement the flushed and horny mother gazed at herself in the large mirror covering one of the walls. Alison was what some would call a BBW. Some might even go so far as to call her an SSBBW. Her long flaming red hair framed a round face that looked much younger than her 45 years. At 5'4" and 250lbs, her huge belly, massive thighs and gigantic ass were only overshadowed by her impressive 46P bra size. No matter how much she worked out, however, she was never able to shift any of the weight. Her workout sessions had begun five years ago, after her divorce from her husband Keith. She had always been an extremely big girl, and Keith had worshipped her curves from the moment they met in college, so her size hadn't been a factor in the divorce. In fact, the two had parted ways quite amicably, both of them realising that although they cared deeply for each other they no longer made each other happy as partners. Keith's booming architecture business meant that Alison had never had to work since she graduated with her degree in Literature Studies, and even after the divorce he happily continued to provide for her and their three children.
Children who were now fucking each other, or at least two of them were. An image of her younger daughter, 18 year old Sophie, gagging on her brother's huge cock flashed through Alison's mind and her nipples were suddenly rock hard again. She studied her body in the mirror more, noticing all the similarities between herself and Sarah. The two of them had been mistaken for sisters before. Sarah had seemed to take the entirety of her genetic makeup from her mother. Same height, same flaming red hair, same piercing blue eyes, same soft pale skin and same BBW body. The only difference between the two was that without the effects of age and childbearing, Sarah had not yet reached her mother's size. Everything was just a little bit smaller on the 25 year old. Belly, thighs, ass and boobs. Having taken her daughter shopping on more than one occasion, Alison knew her bra size was a 40KK.
Sophie had also inherited some of her mother's features. Her blue eyes and pale skin were where their similarities ended, however. Sophie was a petite 4'7" and seemed unlikely to get a late growth spurt. Her hair was an almost white blonde that neither her mother or father could figure out the origin of, since Alison's parents were also both redheads and Keith's entire family sported jet-black hair. Sophie was also extremely slim. She seemed to have the opposite problem to her mother and sister, eating like a plague of locusts without putting on a pound while they looked at a salad and gained ten. At only 80lbs, she had a small rounded butt and wore a 32A bra.
Jason had inherited the most from his father out of the three siblings. Black hair and deep brown eyes. The young man had actually surpassed his father's 6'1" by the time he was 15, and by 18 he had reached his current 6'4". Despite having no interest in sports, Jason had maintained an impressive physique through daily gym and swim sessions since hitting 16, and had maintained the routine in his first year of college. Remembering the scene from the bedroom earlier, Alison thought to herself that bulging biceps and washboard abs weren't the only impressive parts of her son's body. The horny mother hadn't been able to tell how much of Jason's cock had been buried in his sister's gushing pussy, but it had definitely looked to be longer and thicker than his father's admirable 8 inch tool.
As she thought back on the sibling fuckfest she had just witnessed, Alison couldn't help but notice the similarities to herself and her ex-husband. Jason was the spitting image of his father, and Sarah was the twin of her mother. Watching them fuck was like watching an old recording of herself with Keith back in their college days. He had always loved it when she got on top of him, bouncing on his hard cock while he filled his hands with the supple flesh of her belly and tits. She had always cum so hard when he started sucking on her nipples as she rode him, feeling his hands groping every inch of her belly like he would never be able to touch it again. No man had touched her like that since the divorce. In fact, no man had touched her in four years. She had tried online dating a few months after the divorce was finalised and had a couple of hookups before realising that while plenty of men wanted to fuck her, none of them wanted to be seen in public with her. Conversations on the apps inevitably led to invitations to guy's houses late at night. When she got tired of meaningless sex she had started countering with an offer to meet for coffee the following day, only to find herself unmatched shortly thereafter. The experience had made her swear off dating at all, throwing herself into raising the kids and resigning herself to the use of fingers and toys to get herself off.
She needed a real cock though. She needed to feel a man throb as he bust his load deep inside her. Toys couldn't fulfil that need. Not like Jason had fulfilled that need for Sarah. And had she said to him that pushed him over the edge? 'Cum for mommy', wasn't it? Alison sat down on one of the nearby yoga mats and quickly pulled her leggings to her ankles. The smell of her aroused and dripping womanhood assailed her nostrils, and she pulled off her sports bra and began pinching and twisting her nipples with her left hand. Her right hand made its way to her needy pussy, vigorously rubbing at her throbbing clit. She was picturing Jason fucking Sarah, but then it changed. She was watching herself in Sarah's place, impaling herself on her only son's manhood, begging him to flood his mommy's desperate womb with his seed. Knowing the basement was soundproof, she let loose with her moans and groans and dirty talk as she touched herself.
"That's it Jason, fuck mommy! Mommy needs this so bad baby! Plough mommy's cunt with that massive cock and make me my son's incest whore!"
She came as Jason came in her fantasy, the imaginary cum filling her with warmth as her pussy spasmed and gushed. For a few minutes she was in bliss, cumming harder than she had in years, even harder than she had outside Jason's room earlier. When she recovered, she saw that her leggings, thighs and hand, as well as the yoga mat beneath her, were completely soaked in her juices. Luckily the basement home-gym had a built in shower, and Alison always kept a change of clothes down there for after her workouts. After washing herself and changing, she made her way back upstairs and almost walked head first into Jason.
"Woah there mom! I was just coming to check on you, you've been working out a lot longer than usual."
She looked her son up and down. He was the same young man he had always been, same kind and gentle smile looking down on her as always. There was nothing about him that gave any indication that he had just creampied his older sister.
How long has this been going on? She wondered.
