A/N: Hello again and thank you so much for the reviews! Enjoy this last chapter :)

Warnings: Please do not read on if you are underage, if you dislike chan and/or incest, or if you like them, but cannot differentiate between what is fan fiction and what is real life. My stories are strictly for entertainment only and not to be copied or followed or taken as the truth in any which way. Got all that? Please proceed ONLY if you agree with the above.

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Arthur and Molly took one glance at Bill's fully aroused length and swung back to each other, their embarrassment of a moment ago replaced by the gravity of what they were about to do. Molly could feel her heartbeat speeding up and Arthur looked as pale as she felt.

"Move up a bit, Molly," he told her.

"Of course." She shifted backwards and leaned back against the pillows, spreading her legs and keeping her knees bent.

Arthur went to sit cross legged at her side before beckoning to Bill.

"Get on the bed, son," he said. "Sit between your mother's legs, that's right. Molly, could you put your - your-"

Voice failing, he grimaced and waved a hand at her thighs.

"Of course," Molly said again. She raised her legs and rested her plump thighs over her son's slender ones.

Bill looked down at his mother's private parts, so close to his own. He had seen coloured illustrations of the female genitalia in the book, but knowing this was his mother's made him gulp before he looked uncertainly at his parents.

"Now I... put it in?"

They both nodded, not trusting their voices anymore.

As Bill shuffled closer, Molly squeezed her eyes shut. It wasn't that she didn't want this, well, of course she didn't - he was her son! - but she did want the possible outcome very, very much. She supposed that Bill being someone she knew and loved made it both better and worse - of course worse! - at the same time. He was her son and not Arthur and-

A warm palm cupped her cheek, interrupting her increasingly flustered thoughts. She opened her eyes and saw Arthur gazing down at her.

"We've gone over this, Molly. I love you," he said.

Molly's breath caught in her throat and she almost burst into tears right there and then. Yes, this was what she needed other than her husband's presence; his touch and his promise that he was fine with what they were doing. Blinking hard, she gave him a shaky smile and reached up to cover his hand with hers.

"I love you, Arthur," she whispered. She sniffled, pulling in a shaky breath as a gentle thumb wiped away the tear that had escaped.

When Arthur bent down to kiss her, there was only thought going through her head - how much she loved this man. At the sound of a long suffering sigh, they broke the kiss to see Bill regarding them with an impatient yet anxious look.

"Can we get on with it? It's uhm... getting... soft."

As one, they looked at Bill's groin again and then at each other. Arthur's eyebrows went up, Molly's lips twitched and then they started chuckling. It wasn't at Bill's expense, just a much needed release of the tension they were under, but his resultant scowl and furious blush only made them laugh harder.

Yes, they were doing something wrong, something illegal and taboo, something no one should ever find out. But they weren't doing it behind each other's backs and they hadn't Imperio'd Bill or tricked him. He knew why they were doing this and he was participating of his own free will.

"I'm sorry, love," Molly told him. "We weren't laughing at you, I promise."

"No, we weren't, son," Arthur added with a smile as he grabbed a pillow and tucked it under Molly's hips.

Molly adjusted it and then reached down to hold Bill's hand, wrapping his fingers over his flagging erection once more.

"Stroke yourself again, just a few more times. That's right."

Half a dozen strokes brought Bill back to full hardness. Molly took a deep breath and held his hip to urge him closer, shifting her own until he was positioned right at her core. She bit her lip when he gave a small gasp and pushed forward, his head breaching her.

"Deeper," she told him, holding his gaze. She didn't want to look at Arthur. Not now. "Come on."

Bill sank in an inch, eyes widening further.

"Feels... warm," he breathed.

"I know. Go on, all the way inside now," Molly encouraged him with a determined smile. She gasped when he suddenly surged forward and buried himself completely inside her, his thin chest heaving.

"Sorry - did I hurt you, mum?"

"No, you didn't, love. I'm fine."

Molly was more than fine, her body had closed around him, but she gritted her teeth and kept very still. She didn't want to become anymore aroused than she already was.

"It's OK, Molly," Arthur said quietly. "Go on, I don't mind if you enjoy it."

Molly turned to him at once, guilt showing in her eyes. "But Arthur... I - it's not right!"

"Mum? Dad?"

They both turned to look at Bill again.

"I need to move!" he blurted out. He looked desperate, his body trembling and his Adam's apple bobbing up and down as he swallowed.

Molly smiled and reached out to hold his shoulders.

"Lean forward and go right ahead," she told him.

Bill exhaled in relief, his expression almost pained. Bending forward, he caught himself on outstretched hands on either side of his mother's waist and began rocking back and forth, eyes falling shut.

Molly groaned and closed her eyes as well, her hips jerking once in response before she held them still. When something touched her right nipple, her eyes shot open again.

Arthur was worrying her nipple with two fingers and right in front of her shocked gaze, he slid his other hand between her legs and - oh Merlin!

"Not now, Arthur!" she hissed at him, but he just smiled at her, blue eyes twinkling.

Molly moaned in embarrassment and wished she hadn't when Bill opened his eyes to see what they were doing.

"Er... dad?"

"Just keep at it, son," Arthur told him steadily and then he turned to Molly and winked.

Molly glared at him even as she squirmed and panted, torn between wanting to clamp her legs shut, wanting to widen them even more, and wanting to grab something hard to hit Arthur over the head with. The combination of his determined caresses and Bill's frantic thrusts was very quickly bringing her to an inevitable conclusion.

Bill was racing towards the same place for he started moving even faster, cheeks flushed and eyes wide. He looked as if he couldn't believe what was happening to him.

Molly opened her mouth to say something - a word of encouragement perhaps, or a reprimand to Arthur - but the latter gave her nub of flesh a firm stroke and she fell over the edge. She tried to hold back a cry and failed, knees clamped around Bill's hips and her body convulsing around his erection.

Bill tumbled into his own release, gasping and shuddering, helpless against the rush of sensations shaking him. He collapsed onto his mother, panting hard and then two seconds later, shot upright again with a horrified look on his face.

"Something came out!" he exclaimed uneasily. "I... I hope it wasn't my pee!"

Arthur and Molly stared at him in bemusement before Arthur gave a surprised shout of laughter which made baby Ron whimper. All three of them froze at once before turning to stare at the crib, Arthur almost turning purple in the face. Luckily, Ron seemed to have settled down for he made no further sounds.

Bill looked at his chuckling parents and gave a sheepish smile, blushing a bright pink.

"Oh. That was my, er, sperm?"

It was a few seconds before Molly could answer him.

"Yes!" she gasped. "Oh, we're not laughing at you, love. You did very well."

Bill's expression cleared and Molly turned to exchange a look with Arthur, their smiles fading. Their eldest son had just experienced his first orgasm and it wasn't an awkward, exhilarating moment of self-discovery by his own hand and in private, but an experience taught to him by his parents and in their company, for the sole reason of procreation.

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Some ninety minutes later...

The aging potion had worn off. Bill's body was once again nine years old, but he wasn't the same person, his mind and knowledge irrevocably changed by the events of the past couple of hours.

Clad once more in his pyjamas, he sat cross legged on his parents' bed and watched his father cast the pregnancy detector spell on his mother's stomach. The book he had read said the spell would show any positive results as early as one hour after intercourse.

Both his parents gasped as a soft pink glow appeared above the yellow embroidered cotton of Molly's worn nightdress.

"Oh, Arthur, it's pink!"

"I know. I know!" Arthur seemed unable to say anything more as he stared wide eyed at the fading glow. He had cast this spell many times before, but the glow had always been blue. He looked up when he heard a sniff.

"Now, now, Molly, don't cry," he began, but it was too late. She had already burst into tears of joy.

Bill sighed when they started hugging and kissing again, but he didn't interrupt them this time. He turned aside and frowned to himself, wanting to think a bit. He had just had sex with his mother and with his father looking on. It was an experience he hadn't quite managed to wrap his head around. He hadn't been forced into it and he didn't regret it especially with the positive outcome, but it still didn't feel... right.

The other thing that worried him was what would happen when his mother gave birth. He knew this baby girl would be loved and adored by her family, even Arthur whom Bill knew would consider her as his own flesh and blood. But Bill wanted to think of her only as his little sister... and there was only one way to ensure that.

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"Are you very sure, son?"

Bill nodded, looking resolute. "Yes. I am."

"Oh, love!"

Bill fidgeted a bit when Molly squashed him to her. He loved her, but he vowed he was going to marry someone a lot more slender when he grew up. His father might appreciate his mother's voluptuous figure, but he found her curves a bit... much.

Molly released him and pressed a kiss to both his cheeks.

"We can never thank you enough, Bill," she whispered. "Even if the detector spell is wrong and this baby turns out to be a boy, we love you and we thank you."

"We appreciate what you did," Arthur added, sounding choked up. "I... I'm proud of you."

"Thanks, mum, dad," Bill replied. "And I don't regret doing this, I promise. I just don't think I should remember it."

They nodded and smiled with tears in their eyes and then Arthur raised his wand and pointed it at him.

"Are you ready, son?"

"Yes. I am."

Chin lifted, Bill smiled as Molly sniffled and linked her arm with Arthur's free one.

"Obliviate."

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Six months later, a new storey was added to the Burrow and two more rooms created. One of them was Bill's very own.

Three months after that, Molly Weasley gave birth to a beautiful and healthy baby girl christened Ginevra Molly. The tufts of ginger hair all over her tiny head proclaimed her a true Weasley and she was doted on by everyone, from her parents to her six older brothers.

- The End -

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