Couple Devastated After 'Fun' DNA Test Reveals Shocking Result

A US man has been left shocked after taking a DNA test and inadvertently discovering that he is not the biological father of his child due to an IVF mix-up.

Donna and Vanner Johnson, from Utah, decided to purchase a DNA-testing kit for 'a bit of fun', but when they got the results back a month later their whole world turned upside-down.

The pair soon learned that their 12 year-old-son, who had been conceived at an IVF clinic, was not Vanner's biological child after a mix-up at the clinic meant that Donna's egg had been accidentally fertilised by a stranger's sperm.

Speaking to US TV station ABC4, Vanner Johnson said he couldn't quite fathom what he was reading.

"When I looked on that page and saw mum for him and father unknown, I thought 'what do you mean father unknown?'.

"I am his father."

Vanner and his wife Donna underwent IVF treatment in 2007, after they found they were unable to have a second child on their own.

Donna said she first knew something was wrong when the results read their oldest child was only a half-sibling to his younger brother, related through her.

The test revealed Donna's egg had been accidentally fertilised by someone else's sperm during the IVF process.

You understand there's that possibility but it's so remote," Vanner said.

"There were a lot of emotions we had to work through including separating the love of our son which has not changed ... to the issue that we were dealing with."

The couple admitted that they sat on the news for a year before revealing the truth to their son, before embarking on a mission to track down the boy's biological father.

After successfully tracking down the accidental donor, Vanner got in touch and revealed the truth in what he said was 'the craziest conversation I've ever had in my life'.

Both of the couples are currently in the process of taking legal action against the fertility clinic.

Vanner added: "It's grossly inadequate what we are dealing with.

"And as we got going through that process... I thought because of what we are dealing with, it would be treated differently or more gingerly and it's not at all."