Remee, who weighed 5lb 15oz, was blonde and fair skinned. Her sister Kian, born a minute later weighing 6lb, was black.

Both Kylie and her partner Remi Horder, 17, are of mixed race. Their mothers are both white and their fathers are black. According to the Multiple Births Foundation, baby Kian must have inherited the black genes from both sides of the family, whilst Remee inherited the white ones. [...]

Skin colour is believed to be determined by up to seven different genes working together.

If a woman is of mixed race, her eggs will usually contain a mixture of genes coding for both black and white skin. Similarly, a man of mixed race will have a variety of different genes in his sperm. When these eggs and sperm come together, they will create a baby of mixed race.

But, very occasionally, the egg or sperm might contain genes coding for one skin colour. If both the egg and sperm contain all white genes, the baby will be white. And if both contain just the versions necessary for black skin, the baby will be black.

For a mixed-race couple, the odds of either of these scenarios is around 100 to one. But both scenarios can occur at the same time if the woman conceives non-identical twins, another 100 to one chance.

This involves two eggs being fertilised by two sperm at the same time, which also has odds of around 100 to one.

If a sperm containing all-white genes fuses with a similar egg and a sperm coding for purely black skin fuses with a similar egg, two babies of dramatically different colours will be born.

The odds of this happening are 100 x 100 x 100 - a million to one.