Here's my 'genetic impossibility'

I gather that these cats can happen in a couple of different ways. The most common is an XX Y male cat that has one red and one black gene on each of the X's. These cats are sometimes fertile but not always.

Then there is what I think of as the "double mint" cats because he is a "two, two, two cats in one!" In other words "he" is really two cats (twins) who fused together before birth. These cats are also rare but almost always are fertile.

In fact, in one case I read about, the kitty had er...uh...two different color's of well, you know and each one had a different set of sperm when the cat ejaculated.

We know your kitty was fertile as you have living proof, though I don't know if the tests they did on him showed which type of tri-color male he is, the Two Cat theory may be the most likely.

Recent studies have shown that people can be "melded" as well, though since we don't breed as frequently as cats, there are fewer double humans found in the world. When they are, its often because they have two different blood types or other "impossible" biological features. But, like the cats, they seem normal otherwise.