This is not White-crowned Robin-chat (Cossypha albicapilla). Looks like a male of White-crowned Shama (Kittacincla malabarica stricklandii or K. m. barbouri).
If the birds are pure it's stricklandii, barbouri is not in Europe. Most shama's in Europe are hybrids between various subspecies. I'm surprised it took so long for this subspecies to be kept in zoos again, there not that rare in the private bird world