This is Venus the cat.
She has appeared on the popular forum site Reddit.
She looks like this due to a genetic mutation.
“I believe it is a Chimaera. A genetic mutation where two different genetically distinctive "individuals" are morphed into one during embryo development. Basically you'd have regions in the body where the cells can be literally as if they were from another individual, genetically different and can even be different sex altogether.”-DiogenesHoSinopeus
In the same string of comments, the same user responds to a question asking if this can happen to humans as well. “Yes, but not found out very often. Most cases come into light when a mother gives birth, but genetic tests show she isn't the child's biological mother even though she just gave birth to the baby. The mother and doctors get confused and redo the test from another part of the body, especially the reproductive organs, and find out that she indeed is the biological mother to the child she just gave birth to, but part of her body isn't.
Then some cases are found out when the person is giving blood, but instead of having one blood type, they have two different types of blood running in their veins. Some historical documents also mention of people who had limbs of different sizes and patches of skin with different complexion and hairiness.”