Which cranial nerve is responsible for the facial weakness?

CN VII (facial nerve) innervates the muscles of facial expression. It exits the skull through the stylomastoid foramen, enters the parotid gland, and divides into five terminal branches: Temporal, Zygomatic, Buccal, Marginal mandibular, and Cervical ("To Zanzibar By Motor Car"). When only the lower face is affected and the eye can still close, branches distal to the temporal/zygomatic are involved — typical of a peripheral (infranuclear) lesion distal to the stylomastoid foramen.