Becoming a diplomat what majors are good fot this?

I have been reading and someone said that you dont have to be an international relations major to be a diplomat, and the person said she knows two diplomats who didnt study this major International relations, one was a retired dentist and the other an engineer, but got into this field later on. Is this true that you dont have to specifically study this and apply to be a diplomat? So If I do a history major French major Linguistic major could I still get into this Foriegn affairs?