Some mainland countries don't allow registering rhd vehicles, no idea what the situation in Spain is like but he might not be able to register it at all. Should have researched it before he bought the car really! I know that under EU law you must be allowed registration if you're moving from one member state to another, but in that case you must have owned the vehicle for a certain amount of time and the exemption is only valid for the original owner i.e. you cannot sell the car to anyone in the new country of residence.