Since my mum caught me masturbating with my sister's panties, she has made me masturbate in front of her every Saturday and given me her used knickers for the week.

My sister Maddy and I have been having mid-week oral sex as well. Now, three months on, it was a couple of weeks before Christmas, and as always, I was in my parent's room hunting for my present.

When I heard them on the landing, so I hid behind the door of the en-suite Bathroom, just in time. Dad burst into the room, dragging Mum by the wrist, and threw her on the bed.

He stood between her legs and pulled down his trousers and pants. His cock sprang out as he lifted her skirt, pulled her knickers to one side and pushed his full length into my mum.

My mum started moaning and groaning and telling my dad to fuck her harder until she had a massive orgasm. My dad slowed down but continued pumping into her until she said, "Fuck my ass, big boy."

He stopped fucking her pussy and pulled his shiny wet cock out of her. Then he held his tip against her butt hole. My mum begged him to enter her, my dad didn't keep her waiting for long before and pushed his tip in.

They both let out a deep groan as he pushed his full shaft in. My own cock was as hard as his, so I unzipped my trousers and slipped it free and began stroking it.

I started to fuck my fist at the same pace as my dad fucked my mum's ass. They were so loud, my mum's hands gripped the bedsheets and my dad's gripped her hips. They both had red faces and were sweating as they fucked like animals.

Then my dad said, "Here it comes baby, here it comes."

Then he slammed into her ass one last time, and held it tight in her, as his butt cheeks clenched and he let out a deep groan. He stood still between her legs his cock still balls deep in her ass, their heavy breathing started to slow. They stayed like this for a few minutes not saying a word. Then, as quickly as it had started, my dad pulled out his softening cock, pulled his trousers up and left the room.

My mum lay there for a few minutes, her gaping ass hole leaking cum. Then she straightened her knickers, pulled her skirt down, got up and started to leave the room.

As she reached the door, she said, "You can come out now." Then she left the room.

I waited until I heard her talking to my dad downstairs, before I put my cock away and rushed to my sister's room.

I knocked on her door, and when she opened it, I said, "Guess what I saw Mum and Dad doing?"

"You know we're not to talk about it."

"But I need to tell you."

"No, don't tell me just show me."

So I grabbed her wrist, and dragged her to her bed and threw her on it.

"What are you doing?"

"Showing you what happened."

I pulled down my trousers, and my young, hard cock popped out, slapping her tiny pink panties, which made her giggle.

I poked my finger in her pantie leg hole and pulled it away from her pussy and to one side. Then held cock against her lips and pushed in just like my dad did to mum, it was the first time my cock had been inside a pussy, it felt so warm and wet.

"What do you think you're doing to me?"

"Showing you what Dad did. You're so warm and tight it feels so good."

As I pulled out and pushed back in, Maddy let out a little moan. That encouraged me to pump harder and faster like dad.

Maddy was really moaning now and getting really wet. I grabbed her hips tight, so I could thrust harder and harder till she started to cum, screaming and shaking on my cock. When she stopped shaking, I pulled out and pushed against her tight little ass hole.

"No, I don't think so, not my ass."

"But you said, to show you."

"Ok but be careful with me."

So I forced my throbbing purple helmet into her little star and stopped. Maddy screamed and tried to push me out. Once it felt comfortable, I pushed my whole shaft deep inside as we both let out a loud groan; it felt amazing.

I started fucking my sister's tight ass for the first time, I was using my full length and could feel my balls slapping against her. She was now gripping her bedsheets just like Mum did.

Maddy was really moaning, not as loud as Mum, but I thought it was a lot nicer. I was getting close, and I could feel my balls starting to get tight, and my thrusts were getting faster.

I was sweating, and my heart was pounding. I couldn't hold on and fired my first load deep into my sister's tight little ass.

As she felt me cum, she had a massive orgasm, and squirted all over us, we were both soaked. I shot three or four more times.

As I pulled out, I watched my cum run out of her ass, and ran down to her bed. I stood between her sporty legs thinking how beautiful she looked. I could feel my cock shrinking, so I pulled up my joggers.

"That felt great you were so tight."

Maddy straightened up her little panties and then sat up She was still red in the face and sweaty.
She looked up at me and smiled. "Wow, that was my ass, what was that all about?"

"Sorry did I hurt you?"

"Yes, at first, but then I did enjoy it. That's the first time I've done that."

"Everything we've done together was my first time, I'm so happy it's been with my sister."

"What made you do that to my bum?"

"You said don't tell me, show me what Mum and Dad did. I didn't do it as rough as they did it, Dad smack Mum's bum, and they called each other names."

"Yes, Daddy can be rough. Can we try it again tomorrow?"

"Yes, I'd do anything you want, you only have to ask Maddy."