I’ve always had this thing for my little brother’s wife; young, attractive, intellectual, and I suppose, coquettish would be a good adjective for her.

Sure, I love my wife and wouldn’t want to change her for anyone. But every time I see those two little dimples in the small of my sister-in-law’s back, my mind turns to the ovaries that lay somewhere behind them, and I just so want to impregnate them.

My wife, Justine, and I are a little ahead of Mark and Sarah in the family stakes. We have a boy and a girl of five and six. Mark and Sarah have a baby girl, six months old.

For some reason their daughter, Millie, had a blood test; they found Millie’s blood group didn’t fit with their own. The fear was that Millie had been swapped in the hospital, so they had DNA tests done.

The first I knew of the results was a wild-eyed brother on my doorstep, with a sobbing wife behind. I managed to dodge the right hook, but the left jab caught me in the gut, and I sank to the floor.

Half an hour later my wife’s skills in conflict management were being tested to the limit. Sarah was Millie’s mother, no doubt about that, but Millie’s father was a close relative of Mark, a sibling most likely. There is only Mark and I, so I was the culprit.

It didn’t matter how much Sarah and I denied it, and how many dates and diaries we checked, Mark was adamant, I had screwed his wife, and she had my child.

The next time Mark and I met, we were sitting in the hospital consultant’s office, with a security guard standing purposefully behind us.

.

“I have a strange request gentlemen, but please bear with me. I would like a samples from both of you of your blood, your tissue, and your semen,” the consultant said as looked at us over his steepled fingers.

With that, he marked up three vials with Mark’s name and three with mine. Then different nurses led us away to different parts of the hospital.

Another three weeks had passed before we were back in the consultant’s office; this time our wives and no security guard.

“Mark, you are the younger sibling, are you not?” Old Steeple Fingers said, peering over at us.

Mark just nodded.

“Mark, the DNA of your body is different from the DNA of your semen.

Mark stared at Old Steeple Fingers; we all stared at Old Steeple Fingers.

“In medical terms, unused fetal material from your mother’s pregnancy with your brother, has been absorbed by you during your own gestation. Unfortunately it is your genitalia that contains your brother’s DNA.” For a moment Old Steeple Fingers had his audience stunned.

“I’ve been screwing my wife with my brother’s dick!” Mark exploded.

“Well, perhaps not your brother’s penis, but certainly his testis,” Old Steeple Fingers said, and instantly regretted it.

One look at Mark’s stupefied expression and we were all stifling giggles.

“Well, Big Brother, you got another one on me; your spare balls are in me, and I’m just the delivery boy.” Mark high fived me, half in self mocking, half in resignation.

In the darkness before we slept, my wife kissed me on the cheek.

“I know you have always wanted to get Sarah pregnant, looks like you managed it,” Justine giggled and went to sleep.

Mark and Sarah are back together, and we were invited to a BBQ at their home. Mark hugged me the way he used to; it seemed like an age since he had done that.

“Hey, Bro, Sarah and I have decided to try for another baby,” Mark said as we chinked beer bottles.

“Tell you what, Bro, why don’t you cut out the middle man and get her pregnant yourself, doesn’t matter to me. It will be your spunk anyway.” Mark was back to normal, and genuinely laughing about it.

“Then I can try and use your spare balls to get my big sister-in-law in the same state. Makes no odds to me, you will be the dad,” Mark said slipping his hand around Justine's waist roguishly.

I would have taken that as part of the joke, but Justine went very coy, and Sarah had the naughtiest look on her face I ever have seen.

Author's note: This story is based on recent medical evidence and has similarities with a known case. But all characters are fictions.