You've probably heard of chimeras before. They are a staple of the fantasy genre, but they do exist in real life — if a little less dramatically than a riddle-posing Sphinx.
Basically, a chimera is a single individual made up of the cells of two individuals, usually due to embryos merging. Genetically, chimeras are very rare, but among animals the term is also associated with individuals that display two very different color variations in one animal.