What animal does this skull belong to?
Its definitely a bovid, most likely an african antelope specifically a Hartebeest or Alcelaphus buselaphus . There are several sub-species but those horns are a dead giveaway. The the horn do vary a bit by sub-species. The Neumann's or Tora hartebeest might be your best bet but I can't be 100% sure. They are all popular hunting trophies since forever and are even kept in some european game reserves so it is not that hard to find there skulls in private hands. Search "hartebeest skull" and you'll find a million of them so you can try for a more exact match.