Kit Roberts
A pair of twins found out that they were only half sisters, despite being born within minutes of each other.
You might think that few things could be more certain than twins sharing their parents, but two women who were born within just minutes of each other found out that they are in fact not full sisters, as they didn't have the same father.
Michelle and Lavinia Osbourne found out their true parentage after Michelle took a DNA test at home.
While they shared the womb together they in fact each have a different father in an extremely rare set of circumstances.
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This is called heteropaternal superfecundation, and it requires a lot of things which are individually unlikely to all happen together, making the odds astronomical.
The process happens when more than one egg is released during someone's cycle.
More than one of these then has to be fertilised by sperm from more than one partner, and then both embryos have to survive the pregnancy.
It is so rare that only around 20 cases of heteropaternal superfecundation have ever been identified around the world, and Michelle and Lavinia are the only confirmed case in the UK.
Lavinia recalled that she was absolutely devastated when she found out, because she and Michelle had always shared such a close bond after going through a difficult childhood together, including moving around multiple foster homes.
"She was the one thing that belonged to me, the one thing that I was certain about, the one thing that I was sure of. And then she wasn't," Lavinia told the BBC.
Michelle reacted differently to the news saying: "I wasn't surprised. I'm still in amazement that this can actually happen - it's super weird, super odd, super rare - but it makes sense."
Their mom was 19 years old when she gave birth to the twins in Nottingham in the UK in 1976, and had come from a difficult background.
Michelle said: "She had suffered abuse at the hands of [her] stepfather," adding that her mom had been 'in and out of foster care and children's homes throughout her childhood.'
The pair had gone to live with the mom of their own mom's best friend, who they called grandma, when their mom went to London to study at university.
But even after they again saw their mom, they said that their relationship was strained.
"Physically and emotionally, she was always out of reach," Lavinia said.
Eventually, Michelle became interested in discovering who her dad was, though Lavinia said that she had no interest in finding out.
And when the results came back that they didn't share a father, Lavinia said she was extremely upset.
"I was angry with Michelle for having me go through this, because I just didn't want this reality," she said.
Despite the challenges of their situation, their relationship remains strong.
Michelle said: "She's my twin sister. Nothing takes away from that."
"We're miracles. We're always going to have a closeness that can't be broken," said Lavinia.