The identical twin puppies, named Cullen and Romulus, are of the same gender, with very similar markings, which led de Cramer to believe they were identical twins.
Reproductive specialists then confirmed his suspicious by obtaining blood samples from the twins when they were two weeks and then six weeks old.
The puppies have subtle differences in the markings in their fur, because although they have the same genes, those genes aren't necessarily expressed the same way. Just like how identical twins look different to people to know their faces really well.
In total, seven puppies were successfully delivered, but only these two were marked as being identical.