UN Resolution 1244 is the closest thing to international law on record regarding the status of Kosovo and it clearly recognizes that Kosovo-Metohija is a province of Serbia.
It all depends on whether one supports the rule of law, in which case Kosovo is Serbian, or thuggish anarchy, in which case NATO tries to appease the Jihadists.
Can’t say I’m a big fan of the UN myself. “International law” is an oxymoron.