Mysterious planet

Beyond the Kuiper belt, there's a certain planet that humans were not aware of. Her orbit is longer than Neptune, but saner than him. She has 4 big moons, and some little asteroid-like moons. Who is she?

[Planet and the moons are my Ocs]
[Timeline Oc planet appears after the moon revolution]
[Which interaction do you want to see her with? Comment in the chapter and I'll write!]