They keep finding tenth planets and forgetting about them. I remember there was one named after an Eskimo (or Inuit ) goddess in the 1990s, and here’s a new one:
If by “new”, you mean “known for seven years”, and by “planet”, you mean “bigger than another thing that also isn’t considered a planet any more”.
And Sedna and Quaoar were never actually considered planets, because neither is larger than Pluto. Eris (the object you linked, briefly known as Xena before its official name was approved) is bigger than Pluto, and therefore was at the time of its discovery called a planet, but that discovery prompted the change in the IAU’s rules, and now neither Eris nor Pluto is considered a planet.