At this point it seems very likely that there is; however, it has not been officially spotted visually by a telescope. The announcement was the result of years of research by two individuals at CalTech. They propose the planet based on mathematical evidence of something gravitationally affecting small objects on the fringes of the solar system.
This mystery planet, if confirmed, would be recognized as a planet under the current definitions, given that it is likely the size of Neptune, or at least ten times the size of Earth. It's orbit is around the sun, but highly elliptical and lasting 15,000 years.
The theory behind this planet is that it formed with the known planets that orbit closer, but was possibly flung out into dark interstellar space by the gravity of the gas giants, and then slowed down by gas resistance, only to be tugged back into a long orbit by the sun's gravity.
Telescopes are looking for the planet, but given its distance from the sun, the sun is likely no larger than other stars in the planet's sky, so it reflects little if any light.