The evidence supports a planet that is ten times the mass of Earth with a closest approach of 200 astronomical units. The distance between the Earth and the Sun is defined as one astronomical unit. This possible planet is about the size of Neptune, but much farther out. Neptune has an average distance of 30 astronomical units. This possible planet could have an elliptical orbit that takes it much farther out from the Sun.
Note that this planet was NOT imaged. It's too far out to reflect enough light to detect with an optical telescope. The evidence comes from gravitational tugs on the other dwarf planets that are already known. Below is an image mapping the orbit of this possible planet.
This is an exciting discovery, but it's important to be cautious over declaring the definite discovery of a new planet. The evidence looks strong, but more work needs to be done to change our textbooks. Still, very exciting!!!