Worried for relationship and his soon to be born child, the anonymous man took to social media in the search for some advice about how to deal with the situation.
He wrote: "My wife and I have recently discovered that we share the same dad. We have been together for eight years and married earlier this year.
"We own our own home and we're expecting our first child in March 2020. Our bio father is still alive but we don't want anything to do with him because of this and because he was a s****y person."
According to the husband, their father was not a part of their lives and neither of their mums had named the father on their birth certificates.
He revealed their parents have no idea about the situation and said they took a private DNA test which left them in shock at the result.
While the test has rocked them to the core, the husband explained he doesn't want to split up with his wife, but said some challenging times will come regarding their baby.
"Despite this, our feelings for each other have not changed and we do not want to split. We have known each other since starting school and been through some hard times together."
The married couple have no idea what to do after receiving the news. Photo / 123rf
"I am afraid what this means for us and our child, if that means he will have any health complications in life, my wife doesn't believe in abortion personally and does not wish to terminate her first pregnancy (nor do I want her to) so we mean to see it through and hope for the best.
"We are lucky in that we don't have a history of illness in our mums' families at least so hopefully that is better luck than some."
The man concluded: "I am terrified if we could be found out if anyone looked into our histories or if they (I heard they do this) take a DNA sample of our son for genetic testing to make sure he has no health problems and what could happen to us.
"I am not even sure what to do, except maybe ensure that we do not have more biological children even if our child turns out without a problem just to be safe and adopt or something instead.
"I don't want anyone to find out so I am keeping info to minimum and I will not let anything separate us and neither will she. What could happen to us, what can/should we do, should I just bury it?"
A number of readers leapt to the defence of the couple, saying they sympathise with them and believe they're going about everything the right way.
"If you both still love each other, stay together. If you want to keep the child, keep the child. Try not to have any other children. Don't tell anyone about this."
Another said: "I'm so sorry. It's okay to keep this from your mums, it will upset them. Do speak to a doctor about implications for your child. Don't hope for the best, be informed."
Marriage of half-siblings is more common than many people realise.
Often, couples who didn't know they share one of the same parents can suffer from Genetic Sexual Attraction (GSA) - a condition where people fall in love with their long-lost relatives.
