A mum from Bulwell says she is regularly asked "are they both yours?" after giving birth to twins with different skin colours.
When Ayon and Azirah were born at Nottingham City Hospital in April this year mum Chantelle Broughton said she was shocked.
The 29-year-old's son Ayon was born with fair skin and green eyes, meanwhile her daughter Azirah had dark skin and brown eyes. "It was a shock how different they appeared, they're unique," Chantelle recalled.
"People just stop and say 'oh my god', they just look totally different. I've had people ask 'are they both yours?' Although a lot of the time people don't want to say it but when we tell them they say it's crazy as you don't see it very often."
Mum Chantelle says she looks white but is mixed race due to having a Nigerian maternal granddad, whilst dad Ashton is half Jamaican and half Scottish.
There is a one in 500 chance that an interracial couple will have twins with different skin colours, according to population geneticist Dr. Jim Wilson from the University of Edinburgh as reported by the BBC article in 2011.
With the twins now four months old, Chantelle says the pair's complexions contrast more than when they were first born.
"Some people said they'd change but I don't think they will, they are just going to stay the same complexion," the auxiliary nurse says.
She adds: "As time is going on she seems to be getting darker and darker. I think their hair will be different too.
"The girl will have thick and curly hair and the boy's will be completely different. You can already feel the difference in texture."
She said dad Ashton, a 29-year-old construction worker, jokes and asks about them being the delivery driver's children. Ashton said Ayon and Azirah are also different in terms of personality.
"She's quite chilled and laid-back while he's a bit needy," he said. "He doesn't like to just sit there while she'll just lay back all chilled."
Ashton, who was in the room when the twins were born, said he was "overwhelmed" but noted their skin had less of a contrast at first.
He says they have a bright future ahead and added: "It's a bit mad. They both looked quite similar from birth but she is getting darker and darker. She is gorgeous."
Despite many people's amazement at the twins, the phenomenon is not actually so unusual, according to one expert.
Professor James McInerney chair in evolutionary biology at the University of Nottingham's School of Life Sciences, said: "The twins are not identical (monozygotic) twins.
"Therefore, they have different genetics – they are as closely related to one another as two siblings.
"This means they share 50% of their Alleles (an allele is a kind of gene – a specific sequence of DNA).
"In this case, one twin has been the recipient of several of the alleles that might make his skin a lighter colour, while the other twin has been the recipient of several alleles that make his skin a bit darker.
"There is a major gene that is part of a biochemical pathway that changes the amino acid tyrosine into either eumelanin or phaeomelanin.
"Eumelanin is darker and brown, while phaeomelanin is lighter and blond/red. Perhaps alleles for this particular gene are involved and this might make the result look more apparent.
"It probably feels quite unusual because they are twins, but in reality it’s not so unusual."