I have a question for all those have read the books...
In the books, there are several references to Princess Rhaenys having had a kitten - a black one. There are also references to there being a wily, torn-eared, black tomcat that lives in the castle complex. Arya makes mention of him as being the hardest one to catch when she was assigned to catch cats by her dancing master. Tommen later complains to his mother about the "bad cat" that hisses at him and his kittens (also all black), when Cerci asks what he means he says it is a torn-eared black tomcat.
I'm wondering if anyone else has noticed,
I'm putting forth the theory that this cat was once Princess Rhaenys kitten.