A new study has proposed the existence of Planet Y, an alternative Planet Nine candidate that is smaller and closer to Earth than the hypothetical Planet X, which astronomers have been hunting for almost a decade. However, the evidence for this newly theorized world is "not definitive."
That would be quite a surprising find indeed. I’m pretty sure that we would have already observed the gravitational effects of such a planet though. The Planet X and Planet Y the article refers to are out on the fringes of the solar system with Pluto, which is still pretty neat I think.