Currently, the moon is going by the catchy name S/2012 (134340) 1. It joins Charon, Nix, and Hydra, along with the recently discovered P4 (all but Charon were spotted by Hubble). The new moon was spotted in multiple images, making it clear that it was gravitationally bound to Pluto. It’s oddly shaped, varying between 10 and 25 km across.

Ars Technica

How did I not know about Moons #2, 3 and 4, Pluto? ;o;