They were born at the same time to the same mother, but these babies are far from typical twins.
Calder and Alexandra may have shared a womb but, thanks to modern fertility treatment, they are actually half-siblings with different fathers.
The babies were born to London couple Simon and Graeme Berney Edwards via a surrogate they met in Canada.
Advances in IVF meant that the couple were able to fertilise an embryo each, and both were placed into surrogate Meg Stone’s womb. They are still classed as twins, even though they have different biological fathers.